Comparison of wine density and alcoholic strength measurement by hydrostatic balance and electronic density-meter

;

OIV Sub-commissions meelíng (Parìs, 13-15 March, 2002)

COMPARISON OF WINE DENSITY AIID ALCOHOLIC STRENGTH Mf,ASUREMENT BY ITYDROSTATIC BALANCE AND ELECTRONIC DENSITY-METER

Giuseppe Versini, Robeno Larcher, Giorgio Nicolini, and Laura Bologninil

Laboratorio di Analisi e Ricerche, Istituto Agrario di San Michele all'Adige, 38010 San Michele all'Adige 'Unione _{haliana Vini. Viale del Lavoro 8. 37135 Verona}

Key words:

specific $avity Gg)/density (d), alcoholic srength (eS), hydrostatic balance (HB), electronic dendity-meter (!p), methods comparison

SummaTy: _{,l-t 9"À.'\} ('*".l"o[ lt erolo1y (U^io'le ]L [.'arrra, )ttn^.', Vur.,rr^^,I\ Data from pluriannual mglthly ring tests ón wines at different composìtion, organised with official critèria / by an Italian company, have been provided for investigating the repeatability of the specific gravity

measurement of wine using hydrostatic balance and electronic density-meter, as well as, after a proper selection of data according to statistical methods, for comparing reproducibility and precision results for specific gravity and alcoholic strength using both methods. For the first aim, we can confirm the previous results on repeatability in one lab; for the second goal, good linear correlations between results from both measurements with a proper distribution of scores have been obtained, as well as reproducibility values that can fit with some available results for reference methods of EC or by OIV already recognised.

Introduction .

Measurement of alcohol content in wine using electronic density-meter has been recently made official by OIV (Resolution OENO 8/2000) and admitted in the Annex A of the Collection of the OIV Intemational Method of Analyses: repeatability in a proper range (between 4-18Vo Yol), and reproducibility were considered in an inter-laboratory ring test. Besides, both methods referring to hydrostatic balance and electronic density-meter were recognised by EC Reg, n.287012000 as reference methods along with the pycnometry, for the measure of the alcoholic strength of spirits. In the OIV session of March 2001, a Green Paper (F.V. n. 109ó; Cabanis €t al., 1999) concerning an intralaboratory comparison of the hydrostatic balance with the pycnometry to measure the alcoholic degree of wines has been presented. In the same session, the results of- the intralaboratory validation of specific gravity measurement obtained by the hydrostatic balance (EC usual method as in Reg. n.2676190, being the pycnometry the reference method) in comparison to those by the electronic density-meter have been also submitted by Versini et Larcher (2001). Now, we present a compadson of measurement of wine specific gravity and alcoholic strength achieved with the hydrostatic balance and the electronic density-meter, assuming this latter method as OfV reference method for alcoholic strength determination.

Equipments and samples: Equipments:

- _{electronic hydrostatic balance (precision at the 5'" decimal) eventually equipped with a data treatment} device:

- _{electronic density-meter} (Paar-type) eventually equipped with autosampler. Samples:

- wines of different density and alcoholic strength monthly prepared on industrial scale, taken from a bottled stock properly stored, and delivered as anonymous products to the laboratories participating into the monthly ring test organised by Unione Italiana Vini (+eret*'-*e$ according to ISO 5725 (JNI 9225) rules and lnternational Protocol of Proficiency test for chemical analysis laboratories' established by AOAC, ISO and IUPAC (J. AOAC Intern., 1993, 74/4) and after guidelines ISO 43 and ILAC G13. An annual repórt of all tested determinations is supplied by the cited company to all participants.

Results and disctnsion:

According to some validation method rules as in the OIV project final resolution OENO/SCMA/97I84, on each sample a twice consecutive specific gravity and/or atcòtrólic strength measure-.ni *ar carried out by

almost all labs using both methods. Only 3 labs performed all the measurements of specific gravity on several samples using both equipments (Tab. 1).

Results in papers above mentioned proved that the repeatability standard deviation J, and repeatability /, are comparable for both methods measuring both specific gravity and alcoholic strength. As a further validation test, we considered altogether the data of Table 2 îo draw in Fig. 1 the correlation between the two measurements of specific gravity (n. 63 couples of data): r=.99992; sg (HB) = -.00943 + 1.00958 tSg(ED)1. If considering separately as a couple of data the first of one method vs. the first of the other and the second of one vs. the second result by the second, we still obtain very good correlations with the same r's (= .99991 and .99992) and very similar relationships: !g (HB) = -.01033 + 1.01049 tle @D)l and sg (HB) = -.00851 + 1,00866 bg (ED)1, respectively. Sr and r of the two methods are comparable as demonstrated in a preyious intraJaboratory test (Venini et Larcher, 20001).

As for a study of reproducibility, mean and standard deviation for each type of measure and sample analysed (n.27) arc reported in Tab. 2. The data distribution in such triallike test including a rather high number of labs cap approximate the real situation of techniques applied by oenologycal companies and control labs in Italy. Quite all samples have been analysed twice and the total number of analyses is listed. Each series of first and second measurement of data supplied by different labs has been submitted to skewness and kurtosis tests after Barnett V. & Lewis'î. (Ou iers in statistical data, 1984, Wiley, Chichester, UK) - preferred to that of Cochrane to evaluate more then one outlier - to eliminate outliers. The much more numerous labs using hydrostatic balance have been reduced considering only those that supplied data from 199ó to 2000 vintage presenting outliers (significance higher than 957o) at less then 3Vo, and, as for the data of 2000 and 2001, also labs that improved the prformance overcoming such selection criteria.

The data in Tab. 2 were submitted to a linearity test both for the mean values of densimetric measurements obtaining a highly significant linear correlation (r=0.99999; _{sg@B) = -.0002016} + 1.002036 tsg@D)l) (Fig. 2), and of the alcoholic strength with a similar very good linear conelation (e0.99996; as(HB) = .071+ 0.994 taA(ED)l) (Fig. 3), in both cases showing a negligible effect in changing the correlation including or not the sample still as a must for its very low alcoholic strength. For both measurements, optimal parameters for precision and accuracy were obtained.

Plots of scores between each mean value of specific gravity by hydrostatic balance in comparison with that by electronic density-meter, are statistically distributed around zero, with a mean score difference close to the instrument precision for the specific gravity (Fig. 4) or lower for the alcoholic strength measurement (Fig. 5). In these calculations the values referred to the must sample were excluded due to the quite different standard deviation for all the methods in respect to the wine measurements.

The evaluation of the reproducibility standard deviation Sa and reproducibility R - considering the standard deviation of the measurement of each sample as the relevant score of that method for such calculations -indicates similar values for both methods, resulting R in any case lower than the value established by EC Reg. n.2676190, i.e. 0.00045 g/cm'for the specific gravity for sweet wines and 0.19 VoYol for the.alcoholic strength.

Conclusion

The results above discussed proved that t#kat present most spread density-metric methods, i.e. the hydrostatic balance and the electronic density-meter are comparable as for repeatability and reproducibility parameters, as well as for the accuracy also for values typical of products fitting the wine-category, as it was demonstrated for the spirits in EC resulation n. 2870/2000.

Table 1: Measurements of specific gravity and simple statistics of 62 different monthly samples of wines analysed in 3 laboratories with two equipments.

Hydrostatic balance Electronic densitv-meter month year laboratory

code first measure second measure m e a n difference ( 2 n d - 1 s t ) first measure second measure m e a n difference (2nd -1st) 3 1 9 9 9 1 0 1 0.99370 0.99380 0.99375 0 . 0 0 0 1 0 0 . 9 9 4 1 0 0 . 9 9 4 1 4 0.99412 0.00004 4 1 9 9 9 1 0 1 1 . 0 1 1 0 3 1 . O 1 1 0 2 1 . 0 1 1 0 3-0.00001 1 . 0 1 1 0 0 1 . 0 1 1 0 51 . 0 1 1 0 3 0.00005 5 1 9 9 9 1 0 1 0.99460 0.99446 0.99453 - 0 . 0 0 0 1 4 0.99438 0 . 9 9 4 1 4 0.99426 -0.00024 8 1 9 9 9 1 0 1 o.99226 0.99241 0.99234 0 . 0 0 0 1 5 0.99235 0.99235 0.99235 0.00000 1 0 1 999 1 0 1 o.99226 o.99241 0.99234 0 . 0 0 0 1 5 0.99235 0.99235 0.99235 0.00000 1 1 1 9 9 9 1 0 1 ' 1 . 0 1 1 3 31 . 0 1 1 3 31 . 0 1 1 3 3 0.00000 1 . 0 1 1 1 1 1 . 0 1 1 2 1 1 . 0 1 1 1 6 0 . 0 0 0 1 0 2 2000 1 0 1 0 . 9 9 2 3 1 0.99286 0.99259 0.00055 0.99257 0.99249 0.99253 -0.00008 3 2000 1 0 1 1.07392 1 . 0 7 4 0 2 1.07397 0 . 0 0 0 1 0 1.07307 1.07329 1 . 0 7 3 1 8 0.00022 ? _{1 998 24 0.99435 0.99435 0.99435 0.00000 0 . 9 9 4 3 1 0.99431 0 . 9 9 4 3 1} 0.00000 6 1 998 24 1 . 0 1 0 4 8 1 .0 1 0 4 8 1 . 0 1 0 4 8 0.00000 1 . 0 1 0 4 8 1 . 0 1 0 4 8 1 . 0 1 0 4 8 0.00000 7 1 9 9 8 24 0.99241 0.99241 0.99241 0.00000 0.99241 0.99242 0.99242 0 . 0 0 0 0 1 I 1 9 9 8 24 1 . 0 1 2 9 0 1 . 0 1 2 9 0 1 . 0 1 2 9 0 0.00000 1 . 0 1 2 8 8 1 . 0 1 2 8 8 1 . 0 1 2 8 8 0.00000 1 0 1 9 9 8 24 0.99342 0.99342 0.99342 0.00000 0.99332 0.99332 0.99332 0.00000 12 1 9 9 8 24 1 . 0 1 0 1 9 1 . 0 1 0 1 9 1 . 0 1 0 1 9 0.00000 1 . 0 1 0 1 8 1 . 0 1 0 1 8 1 . 0 1 0 1 8 0.00000 I I 1 9 9 9 24 0 . 9 9 3 5 1 0 , 9 9 3 5 1 0 . 9 9 3 5 1 0.00000 0 . 9 9 3 5 1 0.99351 0 . 9 9 3 5 1 0.00000 1 9 9 9 24 0.99365 0.99365 0.99365 0.00000 0 . 9 9 3 6 1 0.99361 0.99361 0.00000 4 1 9 9 9 24 1 . 0 1 1 1 01 . 0 1 1 1 01 . 0 1 1 1 0 0.00000 1 . 0 1 1 0 8 1 . 0 1 1 0 81 . 0 1 1 0 8 0.00000 4, _{1 9 9 9 24 0.99446 0.99446 0.99446 0.00000 0.99446 0.99446 0.99446} 0.00000 6 1 9 9 9 24 0 . 9 9 2 3 1 0 . 9 9 2 3 1 0 . 9 9 2 3 1 0.00000 0 . 9 9 2 3 1 0 . 9 9 2 3 1 0 . 9 9 2 3 1 0.00000 7 1 9 9 9 24 1 .0 1 0 0 0 1 .0 1 0 0 0 1 . 0 1 0 0 0 0.00000 1 . 0 0 9 9 8 1 . 0 0 9 9 8 1 . 0 0 9 9 8 0.00000 8 1 9 9 9 24 0.99241 0.99241 0.99241 0.00000 0.99241 0.99242 0.99242 0 . 0 0 0 0 1 I 1 999 24 0 . 9 9 3 8 1 0.99381 0 . 9 9 3 8 1 0.00000 0 . 9 9 3 8 1 0.99381 0 . 9 9 3 8 1 0.00000 1 0 1 9 9 9 24 0 . 9 9 2 4 1 0.99241 0 . 9 9 2 4 1 0.00000 0.99241 0.99242 0.99242 0.00001 I I 2000 24 0.99372 0.99372 0.99372 0.00000 0 . 9 9 3 7 1 0 . 9 9 3 7 1 0 . 9 9 3 7 1 0.00000 1 1 9 9 6 67 1 . 0 1 1 5 8 1 . 0 1 1 5 8 1 . 0 1 1 5 8 0.00000 1 . 0 1 1 2 4 1 . 0 1 1 2 1 1 . 0 1 1 2 3 -0.00003 2 1996 67 0.99481 0.99481 0.99481 0.00000 0.99483 0.99490 0.99487 0.00007 3 1 996 67 0.99301 0 . 9 9 3 0 1 0.99301 0.00000 0.99275 0.99284 0.99280 0.00009 4 1 9 9 6 67 0.99341 0.99341 0.99341 0.00000 0.99341 0.99342 0.99342 0 . 0 0 0 0 1 5 1 9 9 6 67 1 . 0 7 8 4 0 1.07840 1 . 0 7 8 4 0 0.00000 1 . 0 7 7 5 8 1 . 0 7 7 7 4 1 . 0 7 7 6 6 0 . 0 0 0 1 6 I 1996 67 0 . 9 9 3 1 1 0.993210 . 9 9 3 1 6 0 . 0 0 0 1 0 0.993280.99340 0.99334 0 . 0 0 0 1 2 1 1 1 9 9 6 67 1 . 0 1 2 0 8 1 . 0 1 2 0 81 . 0 1 2 0 8 0.00000 1 . 0 1 1 3 8 1 . 0 1 1 3 6 1 . 0 1 1 3 7 -0.00002 1 2 1 9 9 6 67 0 . 9 9 2 5 1 0 . 9 9 2 5 1 0 . 9 9 2 5 1 0.00000 0.99245 0.99241 0.99243 -0.00004 I I 1 997 67 0.99271 0.99271 0.99271 0.00000 0.99273 0.99263 0.99268 - 0 . 0 0 0 1 0 2 1997 67 0 . 9 9 2 8 1 0 . 9 9 2 8 1 0 . 9 9 2 8 1 0.00000 0 . 9 9 2 7 0 0.99270 0.99270 0.00000 3 1 9 9 7 67 0 . 9 9 3 3 1 0 . 9 9 3 4 1 0.99336 0 . 0 0 0 1 0 0.99348 0.99370 0.99359 0.40022 4 1 9 9 7 67 1 . 0 1 1 4 8 1 . 0 1 1 4 8 1 . 0 1 1 4 8 0.00000 1 . 4 1 1 2 1 1 . 0 1 1 2 1 1 . 0 1 1 2 1 0.00000 6 _{1 997 67 0.99271 0.99271 0.99271 0.00000 0.99272 0.99272} a.99272 0.00000 6 1 9 9 7 67 1 .0 1 0 7 8 1 . 0 1 0 7 8 1 .0 1 0 7 8 0 . 0 0 0 0 0 1 . 0 1 0 3 5 I . 0 1 0 4 0 1 . 0 1 0 3 8 0.00005 7 1 9 9 7 67 0 . 9 9 3 2 1 0 . 9 9 3 2 1 0 . 9 9 3 2 1 0.000000 . 9 9 3 3 1 0.99330 0.99331 -0.00001 o _{1 997 67 1 . 0 1 1 6 8 1 . 0 1 1 6 8 1 . 0 1 1 6 8 0.00000} 1 . 0 1 1 3 4 1 . 0 1 1 2 8 1 . 0 1 1 3 1 -0.00006 1 0 1 997 67 0.99277 0.99271 0.99274 -0.00006 0 . 9 9 2 5 1 0 . 9 9 2 5 1 0 . 9 9 2 5 1 0.00000 4 I 1 9 9 8 67 1 . 0 1 2 0 8 1 . 0 1 2 0 8 1 . 0 1 2 0 8 0.00000 1 . 0 1 1 5 5 1 . 0 1 1 5 6 1 . 0 1 1 5 6 0 . 0 0 0 0 1 z 1 9 9 8 67 0 . 9 9 2 8 1 0 . 9 9 2 8 1 0 . 9 9 2 8 1 0.00000 0.99249 0.99257 0.99253 0.00008 3 1 9 9 8 67 0 . 9 9 4 1 1 0 . 9 9 4 1 1 0 . 9 9 4 1 1 0.00000 0.99448 0.99430 0.99439 -0.00018 4 1 998 67 0 . 9 9 2 9 1 0 . 9 9 2 9 1 0 . 9 9 2 9 1 0.00000 0.99286 0.99288 0.99287 0.00002 6 1 998 67 1 . 0 1 0 6 3 1 . 0 1 0 5 3 1 . 0 1 0 5 8 - 0 . 0 0 0 1 0 1 . 0 1 0 3 7 1 . 4 1 0 4 4 1 . 0 1 0 4 1 0.00007 7 1 9 9 8 67 0 . 9 9 2 8 1 0.99286 0.99284 0.00005 0 . 9 9 2 5 1 0.99251 0 . 9 9 2 5 1 0.00000 1 0 1 9 9 8 67 0.99336 0.99336 0.99336 0.00000 0.9933s0.99335 0 . 9 9 3 3 5 0.00000 11 1 9 9 8 67 0 . 9 9 3 1 6 0 . 9 9 3 1 6 0 . 9 9 3 1 6 0.00000 0 . 9 9 2 9 1 0.99303 0 . 9 9 2 9 7 0 . 0 0 0 1 2 1 2 1 9 9 8 67 1 .0 1 0 4 8 1 . 0 1 0 4 8 1 . 0 1 0 4 8 0.00000 1 . 0 0 9 9 2 1 . 0 0 9 9 1 1 . 0 0 9 9 2 -0.00001 I I 1 999 67 0.99376 0.99371 0.99374 -0.00005 0.99334 0 . 9 9 3 3 1 0.99333 -0.00003 2 1 999 67 0 . 9 9 2 9 1 0.99282 0.99287 -0.00009 CI.99247 0.99254 0 . 9 9 2 5 1 0.00007 J 1 999 67 0 . 9 9 3 9 1 0.99386 0.99389 -0.00005 0.99359 0 . 9 9 3 6 1 0.99360 0.00002 4 1 999 67 1 . 0 1 1 6 3 1 . 0 1 1 6 3 1 . 0 1 1 6 3 0.00000 1 .0 1 0 7 3 1 ,0 1 0 7 8 1 . 0 1 0 7 6 0.00005 7 1 999 67 1 .0 1 0 2 8 1 . 0 1 0 2 8 1 . 0 1 0 2 8 0.00000 1 . 0 0 9 7 8 1 . 0 0 9 7 4 1 . 0 0 9 7 6 -0.00004 I 1 999 67 0.99256 0.99261 0.99259 0.00005 0.99240 0 . 9 9 2 3 5 0.99238 -0.00005 1 0 1 9 9 9 67 0.99256 0.99261 0.99259 0.00005 0 99240 0.99235 0 99238 -0.00005 1 1 1 9 9 9 67 1 . 0 1 1 6 8 1 . 0 1 1 5 8 1 . 0 1 1 6 3- 0 . 0 0 0 1 0 1 . 0 1 1 1 3 1 . 0 1 1 2 2 1 . 0 1 1 1 8 0.00009 1 2 1 9 9 9 67 0.99336 0.99336 0.99336 0.00000 0 . 9 9 3 1 7 0.99327 0.99322 0 . 0 0 0 1 0 2 2000 67 0.99251 0.99246 0.99249 -0.00005 0.99220 0 . 9 9 2 4 1 0 . 9 9 2 3 1 0 . 0 0 0 2 1 4 2000 67 0.99386 0.99386 0.99386 0.00000 0 99375 0.99380 0.99378 0 00005 5 2000 67 1 . 0 1 3 2 8 1 . 0 1 3 2 8 1 . 0 1 3 2 8 0.00000 1 . 0 1 2 7 6 1 . 0 1 2 7 0 1 . 0 1 2 7 3 -0.00006 mean std.dev f : ù 0 1 4 1 1 . 0 0 1 4 2 1 . 0 0 1 4 2 0 . 0 0 0 0 1 2 0 . 0 1 6 1 2 0 . 0 1 6 1 2 0 . 0 1 6 1 2 0 . 0 0 0 0 8 5 1 .0 0 1 2 5 1 .0 0 1 2 6 1 .0 0 1 2 5 0 . 0 0 0 0 1 7 0 . 0 1 5 9 5 0 . 0 1 5 9 8 0 . 0 1 5 9 6 0 . 0 0 0 0 7 8 Sr r 0.000061 0 . 0 0 0 1 6 9 0.000056 0 . 0 0 0 1 5 7

-l o' g 6' !Y U) 5 p o (t, o) à (n -o U' o CN E o o o (o o) 5. g) J o. g) d o :t o c) CI' é (o o N ! CÍ' 0) 3 1t 6' o o) 3 o) CN (D o-:i' o I d ct o il o

a

f (o o q :'+ U) o il ct, o 0) x f I a € l l (t, É (D o N) (f o N) () O N) o O N) o O J N) O O J N o O O N) o O o N) O o O N) O o O N) o O o N) a O O N) o o o N o o O N) o o o N) o o O (o (o (o J (o (o CO CO (o (o (0 (o (o (o (o CO (o (o (o (o (o (o (0 (o (o (o @ (o (o (o (o (o (o (o oo)a D f a l) n (tl à (t N) _{N) O} (o \l O) (Jl è N) _N)A J_O (o \l O) (Jl s (r) N) J

$ 5

3 = 9 - 3 o .q-a o o. É t l nI a o = ù v I c]

I

o a7 n I o € in (' € ù 7 I o na € € (n î) I U) € v I I É n I o T@ €I a o I U) É = nI g n I a (f, € nU' €_t a) o I a É vI 0 € nU' € 5' o E o É J o n o il ?) I Ì\) (, O qc (o N) { O (f (o (o s à (tl O qc (0 N) @ (o O to (o N) (J| @ o (o (o o) ! O) b o) o J O io (o N O O io (o s o (o CO (, o CO O Co (o N) à è b OJ o ! o (o CO (.r) o O) O iio (o N) (, (l) o to (o (r) ('r o, o <o (o (, J { t) à s (f io (o t\) s @ o io (o CÀ) O) { b J o o N) o to (o N N) (tl P (o (o s N) ('l J b J o, o to (o o) O) (o O (o (o tv { à P (o (o (, (tl { 3 o 0) 3 q) -a d U' 0) * o (t o) F = a o o o C) o q'

o

N o o o ro o 3 (r) a o o fD U O b o O J (o (o o b O o (Jl N O t) o o J { N) O b o o J O (o O b o o o @ o b o o à (o o O o O N) @ O) O b o o j $ (D I O o O (, (,l P O o O (rl O) O b o o J (Jl { O t) O O N O) ! o b o o (rl t\) o c) o o à (, o b O o J o, o b o o t\) @ O b O o à N O b O o (D (, o b o o @ J o b o O N) o O b O o J N) à o b o o (o o b o o O O b o o N) è O t) o o o (o à O b o o o @ (n o b. o s il ct, o o) (, o (,O N)@ N(0 (.r)O) (t O N)@ N) \t t\)@ (J) o, (,^)(, 5tv èN) (, ! o)('l (,(Jl (.^)O (, 5 (,! Ca)@ (^) (oÀO N)@ àO CÀ)(, cù@ 9) o ) 1 # o ó + r a c) o l l b J (.ù J O iro (o N) o, { O io CO à à À O (o (o N) @ @ O Co (o N (J| o o io (o o) { (o t) N) (o O) O Co (o J N) @ o at (o à s O (o (o ()) O o) O (c (o l\) À à b (f) O o (o CO (, @ J O (o (o l\) o) à P (o (o (, o, O) O io (o (, (o b J (,.) O) o (o (o l\) À N) O qo (o (, \l o J b O (o (o (, o Co (o N N ('l O eo (o à N) (o b o @ O (o (o Ca) { O (o CO N o) (,À) I(o CO (, ('l À 3 o 0) a (t m o o d 6' o. o = o I 3 o o O t) O O (Jl À O b o O O O) O b O o c) (o o o b o o O N) o b o o O (o O) o b O O O @ O b O O A @ è O b O O J O N O b O o O À O b O o o O) N O b O o N O) o b O o N) N) (o O t) o O O O) N) O b O o (, (^) o b O o J J à O b o O o \l (rl o b o o (tl N) O b O O o O) O) o b O o o (o { o b o o @ CJ| O b o o o) o b o o { o b o o { { (f e) a o f\) o (.) o b o O (r) { o b o o (/) o) Q o-i2. o o) N) (tl @ o)(o (tl ('l ('l(, À\l (tl J à (tt èN) (,t) co sO (À)(o (,^){ (,@ CÀ)à N)(o (, (tl (,(tl (.r)(.\)(,@ 5 o (,^)(o (,_à o)(o N)(tl CD_o q)

E =

CN I o o O O O o) o b O O O (l) o b o O O t9 O t) O o O O b O O o @ I O b O o o CÀ) o b o o o (Jl I o t) O o o @ I o b O O o (, o b o o o G) O b o o o O O b o o O { o b o O O (Jl I o b O O o A I O L) o a o I O b O C) o O t) o o o (o O b o o O (tr I o t) O o o G) O b o o O (o O b o O O o I o o o o o o) O b O o o (o I P o O o o o b o o J o b O o o C}) ft) I q @ b o) J L^, u) J J bot^, (Jl bJ G) { b (Jl L^,_{ N) b (, O bo (Jl J -! { à À N) N) l\)à a^,o bo { b, @ t)_s i\J(, @ b O J J N) \J J * CO { b, o, J fo s J J i\J (tl bÀ 3 o À)₌ -o ó Q o) o o o) ot = o o o o o o o o 5 o O b o) @ O b { O O c) (o O) O b { O b @ N O O { (tl o O @ (l O k) (o @ O b @ à O O O) (Jl o b @ @ O b (tl CÀ) O o \t { O o o) @ O o @ o) o b O) o b (o O b (o (, P J O I O J o o (o (/) O b (o @ o b (Jl o) O b (tl @ o b { o) O b (tl À @ o-b. o o) à (tO l\)@ (J) N (r) à (,O (,O (^)O N)è N)@ (,^) O Ca)N) (r) N) 1\) @ NO) N) @ N)N f\)O) (, 1\) (j) (,.) à o)N) N) è (/)J N) (tl N(o q) $ - ^ à o ó + ' o @ b o) J L^, À boo) o)N) À(, C.)N) { b J J L^, (tl J io (o O @ à -@ { À (J) A t J N J i.J à J i.J (tl J b Ò { b (tl J b l\) J i\J o) @ b (l) i,o c) -(o { b s io_! i\J(Jl b(.r) 3 o o)₌ @ m i6'' o d = c) o o 3 @ 3 o (D o t) \,1 o b_\.| tv O a) O) (o O b (tl O) O b (tl à O t) (Jl ('l O b o) 1\) O b O) (tl o b (o N) I o { O) () t) \l ! P O (o J O b à (o o b (Jl \t o b (Jl J O b O) (o () b (tl o O t) o) O t) CÌt (o O b o, o b ('r O b O) O) o b s @ o b ('l (o O b (o N) I o o à cn o b. o

s

o = (Jl o) o,N) O)@ (tl @ (rl @ à(o ('| à C^)à àè èO Ào, ÀN) Ca)@ OJ { àè (, èN) (,@ G)è Àf\) àf\) 5 N) (,{ èÌ\)(,){ (r) o) o) s - o

E =

v, O b O I O b I O t) t\) O o (/) I O o 1\) O o O t) 5 O o N) O b à O b Ob O o t b J O o O o b (, O O O o b à O b N) o b O I O b (, I O b (,D o O O o ?) N) I O o o) O t) O o b J I @ 3 o 0) o 3 * ^É a CL II

n s 3 5

o o b i o o ( o o { o à o i o) ot P P 9 P o o o o o o o o o o o o (^) r. o .a r ' l } . ( , t . . T J C D O o o b i o o ( o (0 (.) o ( o o ) @ o o o o b b b b o o o o o o o o N O O J ( ' ) ( 0 è N o ( . ) à à 9 9 o o o o o o o o Olt .À crr (,r . d

$A

9 9 P 9 r o o o (rr (rr .ò { f o { o ) ( o i ' È

HA

o o o o s b i r b (, È ..ò o) N { ( . ) o ) P P o o N O (.) (rr O b o N) (, ('l O O b o N) l.o (o G) O b O O O)

Figure 1: Regression

line of the specific

gravity

computed

on the basis of the mean value of 2

subsequent

measures

carried

out on samples

(n=62)

analysed

in 3 different

laboratories

0)

o

c

$ $

-o

o

(0

a

o

o

:E

1 090

1 080

1 . 0 7 0

1 . 0 6 0

1 . 0 5 0

1 . 0 4 0

1 030

1 . 0 2 0

1 . 0 1 0

1 . 0 0 0

0 990

0 . 9 8 0

O O O O O O O O C ) O O O @ O ) O C ! C O $ L O ( O | ' - € C | ) O ) O ) O O O ( ) O O O O O O O O - - - =- - ; - ; -

-E lectron

ic density-meter

1 . 0 0 9 5 8 x

- 0.00943

R - 0.99992

o c o p a o c . 9 c) -c o o 6, E o a (l) o -= o-o C o (o 6 t-o E o @ q) F (f) q r N q r t_ o o E I (-) E ' a o lC . 9 c o t-o ó c ) (f) E () \ o) O) O) o @ o) o @ q O o q q c{ g r cf) q r (o N t l c O o c) N o .= o tÉ o) c)

'o

o o-a O) (f) rf) N

8 A

o o ) , o )

5 E

( o o K r l

8 L

t l

(ecue;eq cqelsorpAH) _ttuclO

o) q @ q f-q r (o O

-- g

o Q t o t r O I ; à_{' 6} - + C ò o . 9 ,-l O r ( ) o

s g

r Cr) E r C ) q è , O q r o) (IJ O @ O) o f\ N t l c C) o N $ = o (t) C) 6 o o_ U) a CI o $ o -o ,(o o o ìo c o q) a ; (o L $ a o o,

E

(o U) c o o c o o C) a o a (o (D

E

o o o a -o = o N o o ([ c (o o

E

q) o a , o (U -o o -c C o a o

E

$ o o J

o-E

o

O = o o) (J ' 6 c) o-a o) o O

5

c o , a CN q) ct, o) ú. o.i q) 5 g, IL o D € } f - ( c ) r o \ t c o N c ) o ) @ q o q o q q q q q q q q Y ' r r \ - r r r \ - r o o l a ,

IwJUBIBQ ctlBlsoJpf g) gurc7o

@

5

N R N Y O ) o o ) r O )

X E

d í o R r l

8 ì r

t l

l.l , 7 ' v C A \ u (,

x

o r ^ \.v /T\ a 2 \./ , f = f o 1-'t * t /t\ \ v

gr

\ / ^ v :t v : \ ' / a *-t o @ f o ! Ò + - -_J v O U A -l o € $ * a o 0 ) É 3 : f o U) v l è O . \ O J _,t t+ \ T IÀ' J o o-v --+ì ^\ -.+| y O A 6 a _+ì o ) - i s 6 1l -! { D i , t + \ Y O 0 ) J

I

v' 0) -/n \ v arv ...h N) (, c C' U) o n (-O :l + 1 ) o ^ r ry o C -1 o a n l w = . /fi \ v l-c * v f o / o _{Y o l ( H y d r o s t a t i c b a l a n c e )} o J N u ) . a ( r o . ) ! @ ( o d ì 3 ; , l : l \ . / l , A i - i ' l r l NJ o -r = - r r l l 6 r o o 4 l l . a O Q X A r l : l i x x w r T ( o î ( o o o ) r : . - ! Y N ) J o -3 I I N) \] s a /^t /h

tr

o C ) o ) /_l i : ) \ : \ , r o t O r J , @ ' | 3 ( o , o + o r v _o J J r L__ À N) J o / o _{v o l ( H y d r o s t a t i c b a l a n c e )} J J J @ ( O O J N J À n r l > N / . l ^ l l i n O -( o ^ / A V v r = w >< a ^ \ / r ^ î t ^ w w t ! o q * . ^ \ yÀ ! X f + t ^ î ^ U \ g + :t q) & N) C) o o "1 ' t l r! /î\ @ \o f c o o o l . r O O o a a l . r = o N) J -j :t o a I /n ;i *. f o f ìo f J J Q o) ,î-J o ;i { o (t tl, o = =: @ o (o = o) J L -À

I

O

o

o

.J (tl

s)

O

o

o

-À

o

9

O

c)

O O (tl

P

O

o

o

O O t t !

P

P

S

)

o

o

o

o

o

o

O O O -'a "A' _o (tt o ('l

T1

(o'

c

. g d

J È

: a

_{-r lo}

o o

@ . 1 - 1 FI $ =

É o

o ( o

r E

0 r à

=

o

o ( o

6 - ì

\ / = $ (^) : f Y

o- o_

o +

_{_t}

o o

s d

-l qt

q d

= . o

c ) a

o- (r

o ( D

-l

r-{-6 É

= o

5 o

i =

-, -!

O

J

q E

...1 -,

g o

-o)

3 t r

ll o)

N ) o

o ) J

\'/

_6'

o

o-o l o

g

3

o 0) :f, 0) I o t l I O O O O ()l (o o

3

(,

0 . 9 9 1 2 8

a 99225

0.99234

0.99242

4 99244

0 99250

0.99263

o.99267

0.99288

0 99306

0 9931

9

0 99354

0 99366

0 99370

0 99371

0 99379

0 . 9 9 3 8 1

0 9 9 4 1 4

0 99429

o 99444

1 00993

1 0 1 1 0 8

1 .0 1

1 3 1

1 0 1 1 3 6

1 . 0 1 2 9 6

1 .0 1 3 0 1

a

E

o

o

'.+ì

o '

(o

-l 0)

.-{-(t

m

ó-o

,-+ -l

o

5

o '

o-o

= @ ,-+ I

3

o

.+

o

-|

l t t l

9

9

P

9

9

P

9

P

p

P

S

)

O ( ) O O O C ) ( ) O O O O À C ù t $ r O - - \ N ) ( r À ( J t O ) T1

(6'

c

-l

( r o

-?

O - o

d s

# 4

d . o

o t n

( r +

$ o

q a

ó +

o :

t s

$ o

"î J

o-o q

E #

\ t <

+ o i

o

f

f

o

F ' O

; @

q F

ú 3

f E

3 : r

g 3

(D (D

-r

o)

_-f

g ;

0)

-l _.+

i o )

N) O)

o ) c )

5

6 '

o

o-8 0 3

7 6 1

8 0 6

o

o 1 1 0 0

5 ,^f

= 1 1 0 2

O l

g 1 1 . 0 3

d

;

5 1 1

. 1 8

(o

5 1 1 1 9

(t

l l l ,

9

1 1 2 3 ,

-|

o 1 1

. 2 4

f

\ ' 1 1 . 2 5

o-5 1 1

. 2 s

@ l -:.

q 1 1 3 0

t ,

I

d 1 1 3 2

e' 11

32

1 1 3 4

1 1 . 3 5

1 1

. 4 3

1 1 8 3

1 1

9 7

1 1 . 9 9

o o o)

3

o 0) f I

r . - E

t l . O O c) À O)

s

o

m

tPl

g]

L