T H E J O C R N A L OF I N D C S T R I A L A N D ENGINEERING CHEMISTRY
Apr., 1916
TABLEI-DATA
LAB.
No. 3054 3060 3066 3073 3081 3103 3112 3132 3148 3179 3201 3220 3244 3255 3284 3298 3308
Date analyzed 1911 Aug. 23 Aug. 27 Aug. 30 Sept. 3 Sept. 6 Sept. 10 Sept. 13 Sept. 17 Sept. 20 Sept. . 2 4 Sept. 27 Oct. 1 Oct. 4 Oct. 8 Oct. 15 Oct. 18 Oct. 22
ON
Specific gravity 1.0648 1.0662 1.0670 1.0721 1.0731 1.0746 1.0817 1.0824 1.0724 1,0827 1.0831 1,0737 1,0690 1,0626 1.0750 1,0726 1,0741
THE OCCURRENCE O F SUCROSE IN A SEEDLING GRAPE(J. R . RESULTSIN GRAMSPER 100 Cc. OF JUICE Total solids 16.80 17.17 17.38 18.71 18.97 19.31 21.23 21.41 18.79 21.49 21.59 19.13 17.90 16.23 19.47 18.84 19.23
Sugarfree solids 2.24 1.86 1.87 2.04 1.95 2.00 1.96 2.36 2.08 2.02 1.83 1.95 2.21 2.08 2.30 2.28 2.32
Invert sugar 7.90 8.56 7.91 8.27 8.32 7.97 8.91 9.15 8.99 9.52 9.51 8.96 9.31 8.92 9.72 9.43 9.40
Sucrose Total Total by sugar acid as inversion a s invert tartaric 6.66 14.91 0.56 6.75 15.67 0.50 15.91 7.60 0.42 8.40 17.11 0.39 17.48 8.70 0.42 9.34 17.80 0.47 0.30 10.36 19.82 19.57 0.34 9.90 17.12 0.26 7.72 0.30 9.95 19.99 0.26 10.25 20.29 0.21 8.22 17.61 0.31 6.38 16.03 0.29 5.23 14.43 0.29 7.45 17.56 0.24 7.13 16.93 17.31 0.25 7.51
mild, honey-sweet, not exactly grape-like in character, yet many persons have pron.ounced it as very pleasant and desirable for table use. I t can be harvested for market over a long period b y selecting t h e bunches. Table I gives the chemical d a t a in full, with notes on t h e character and condition of the fruit when analyzed. Our thanks are extended t o Dr. B. G. H a r t m a n n who has aided us in this investigation. The d a t a herewith published complete three years’ examination of this peculiar grape and quite fully cover the question of its composition. The further question of its practical value belongs t o students of horticulture. BUKEALJ OF CHEMISTRY,
\vASHINGTON
A COMPARISON OF METHODS FOR’l’HE DETERMINA-
TlON OF CASEIN IN MILK By C . B. HERSEY Received October 20, 1915
Xs a part of a. milk study’ which was ComPletedbY t h e author during the past year a t the VniL’ersitY of California three methods for the determination of casein in milk were compared. T h e folloking rGsum6 of t h e work is now submitted with results: Ever since Dr. Babcock introduced his remarkably simple and accurate method for fat determination in milk, much effort has been spent on devising Some equally simple and accurate determination for casein in milk b y which t h e cheese maker could more carefully Control his product and b y which the dairyman could receiye a more equitable return for his milk. From among the SeVeral methods thus evols’ed t h e ones chosen for this comparison were t h e T‘an Slyke t h e H a r t Centrifugal3 and the Official Nitrogen or Kjeldahl m e t h ~ d . A ~ systematic comparison of t h e above methods had n o t been made, though the Shutts and ~~~~6 each made a few tests H a r t and t h e Nitrogen method, Literature 1 “-4 S t u d y of Milk from Individual Cowsshowing DailyandSeasonal Variations in Composition and a Comparison of Methods f o r the Determination of Casein in Milk,” being a thesis on which with other work the author was granted t h e M . S. degree in Food Chemistry, Univ. California Library, Berkeley. 2 L. L. Van Slyke a n d A. W. Bosworth, “A Volumetric Method for Casein Determination in Milk,” N.Y . Exp. S t a . , Tech. Bull. 10, 231-241. E . B. H a r t , “ A Simple Test For Casein in Milk a n d Its Relation t o t h e Dairy Industry,” Wis. Exp. S a . , Bull. 166, 22. 4 “Methods of Analysis of t h e Association of Official Agricultural Chemists.” U. S. Dept. of Agr., Bur. of Chem., Bull. 107 (Revised), 1 1 7 . 5 F. T. Shutt, “ H a r t ’ s Casein Test.” Canada E x p . Farm. Rpt., 1909, p . 192. H . H. Dean, “Comparison of H a r t ’ s Method,” A n n . R e p t . of Onl. A g r i . Col. and E x $ . F a r m s , 34 (1908). 97-127.
33 5
EOFFA N D S . F. SHERWOOD,ANALYSTS)
CONDITIONOF FRUIT Berrieslarge, fine condition, not fully colored Aboutsamecondition Maturesunevenly. some bunches appear fullyvipe Aboutsamecondition Continues t o develop very unevenly Condition holds as for previous d a t e Ripeningunevenly S o m e b u n c h e s p a s t best condition Condition holds, some bunchesnot fully colored Crop picked for market Flavor becoming peculiar, not vinous Fruitholdingwellonvines Fruit h o l d i n g w e l l o n v i n e s Fruitholdingwellonvines F r u i t h o l d i n g w e l l o n vines Fruit falling Fruitfallinghadly
paring t h e Van Slyke and Official or t h e Van Slyke and t h e H a r t method seems t o be lacking. METHODS OF ANALYSIS M E T H O D was performed exactly as given in the bulletin,’ using t h e chemist’s modification, t h a t is, N / I O acid a n d base instead of acid of an arbitrary strength. H A R T METHOD-The details of procedure were followed exactly as given in t h e bulletin with the exception t h a t instead of using hand power t h e centrifuge was electrically driven ”with rheostat for speed control, which feature is greatly to be desired not only from a muscular point of view b u t because of t h e greater uniformity of speed attainable which is essential t o t h e success of the test. NITROGEN M E T H O D was carried out according t o the Official Kjeldahl-Gunning method. In t h e latter part of the work j per cent of CuSOd was added t o t h e K2SO4 (Hibbard’s mixture)* which expedited greatly the time required for the decomposition with the strong sulfuric acid with exact117 the same result. as f a r as nitrogen is concerned, Throughout the work all directions and precautions were carefully observed. Frequently full duplicate analyses were made,
VAN
SLYKE
RESULTS
Table I shoL?Ts t h e average for each method of 1 4 3 , samples of fresh each analyzed by the three methods, with a maximum and minimum f o r each method. ~h~ close check of the ~~~t and official b y the average and the corresponding doubt. ful check of t h e v a n Slyke and Official are t o be noted, TABLEI Official Average.. . . . . . 2,477, Maximum . . . . . 3 . 3 1 Minimum. . . . . . 1 . 7 1
Hart 2,52VC 3.4 1.81
Van Slyke 3.077, 3.70 1.05
Table 11 gives in detail the variation of the two methods from t h e Official method which is considered for t h e Comparison t o be t h e standard of accuracy. T h e variations are given in percentages of casein, showing t h e number and percentage of determinations which differed b y various amounts both more and less or higher and lower for each method t h a n b y t h e Official method. Cnless this “higher and lower” factor be determined it might be possible t o arrive a t a series of averages which would give an erroneous impression of t h e true condition; i. e., in any individual 1 LOG.
Cil.
P . L. Hibbard, “ATotes on t h e Determination of Nitrogen b y the Kjeldahl Method,” THISJ O U R N A L , 2 (1910). 463-6. 2
T H E JOURNAL OF INDUSTRIAL A N D ENGIXEERING CHEMISTRY
336
average half the d a t a might be high and half low, with none near t h e mathematical average and great differences between. I n Table 11, however, this factor is taken care of and this table gives t h e complete d a t a as t o accuracy on each of the two methods as compared with the Official determination, all three analyses being made on the same milk sample, with the addition of a fem odd pairs of determinations TABLE I1 Variations in Per HART METHOD cent Casein from DETERMINATIONS Official Method hTo of yi of (0.0 to0.1 60 40.5 MORE 34 23.0 THAX 2 1.4 BY i 0.3 to 0.5 4 5 OFFICIAL 0 . 5 t o 1 . 0 1 0 .i METHOD 0 0.0 EQUALTO OFFICIALMETISOD 9 6.1 ( 0 . 0 to 0.1 25 16.9 LESS 0.1 t o 0 . 2 i 4.7 THAN 0.2 to 0.3 1 0.7 BY 1 5 0 . 3 t o 0 . 5 2 OFFICIAL 0 0.0 METHOD 0 . 5 to 1 . 0 0 Over I . O 0.0
i
TOTAL
-.
VAN SLYRE METHOD DETERMINATIONS K O . of % of 26 18.2 21.0 30 11.2 11.9 10 7.0 11 7.7 2 1.4 16 11.2 9 6.3 1 0.7 2 1.5 2 1.5 1 0 7
;;
~
143
148
(where a third analysis ‘ems lost) but which in no way affects t h e accuracy of the results. Thus from Table I 1 it would seem t h a t as to accuracy the H a r t method f a r exceeds the Van Slyke method both in smaller total average variation from the Official and in t h e number of determinations with much variation. I t is also seen t h a t while approximately 7 5 per cent of the H a r t determinations check t h e Official method t o within 0.1 per cent, only 36 per cent of the T’an Slylie determinations check within t h e same limits. It was also found t h a t where there was TABLEI11 TOTALTIXE TO COMPLETE PERSONAL METHOD VARIATION AVERAGE (a)31/2 Hrs., Official 3-6 H r s . } ( b ) 5 Hrs. Hart 15-20 Min. 15-20 Min. Van Slyke 15-90 Min. 45 Min. ( a ) With I l i b b a r d mixture (6) With electric centrifuge
.4TTENTlOK REQCIRED VARIATIOR AVERAGE 20-60 Min. 40 Min. 5-15 Min. ( c ) S Min., ( d ) l 5 hIin. 30 Min. 20-60 Min.
(bj Without Hibbard mixture ( d ) Without electric centrifuge
a maximum variation between t h e H a r t and Official methods of 0.54 per cent casein, there were 1 2 determinations by the Van Slybe method which varied over I per cent from t h e Official, with one maximum variation of 1.88 per cent. Table I11 shows t h e comparative rapidity of t h e three methods based both on consideration of the total time required from beginning t o completion of t h e test, and on the actual time which the analyst would have t o give the test in undivided personal attention. This table gives t h e approximate figures showing the time required t o make the determinations after all standard solutions are made and t h e analyst has acquired a fair degree of proficiency in the methods. Table I11 shows in a rough way t h a t not only is the H a r t method greatly superior t o t h e other methods as t o rapidity b u t t h a t there is little choice in the actual time of personal attention required between the Kjeldahl-Gunning and the Van Slyke methods. Especially is this so when t h e Hibbard mixture is used with the former. I t must be borne in mind, however, t h a t in total time required the nitrogen method is much longer t h a n either oE the other methods. Furthermore, the H a r t method required not only t h e
Vol. 8 , NO. 4
least total time b u t also the least personal attention; i. e., barely five minutes with electric centrifuge. CONCLUSIOP;
accmacu-Though the Official Nitrogen method is t h e standard of accuracy for the determination of casein in milk, t h e above results show t h a t for all ordinary work t h e H a r t method with electric centrifuge is dependable. checking very closely t h e Official method. and is far superior t o t h e Volumetric method. RAPIDITY-& t o the time required by t h e three methods, t h e Official is longest in total time, with about the same time required in personal attention as t h e Van Slyke method. The H a r t method requires, however, b u t a small fraction of t h e time of the other methods and has t h e added advantage of requiring neither exactly standard solutions nor final calculation of results. THE GRIFFIN-HERSEYLABORATORIES 754 S. Los ANGELESSTREGT, Los ANCELES
SOME CHEMICAL CHANGES IN THE RESWEATING OF SEEDLEAF TOBACCO By HENRYR. KRAYBILL Received Kovember 4, 1915
Since Nessler’ stated t h a t t h e process of sweating tobacco was a fermentation, much investigational work has been done upon t h e study of t h e agents which induce the process. Numerous conflicting theories have arisen. There are those who maintain t h a t bacteria are t h e foremost agents in producing t h e fermentation, others uphold t h e enzyme theory and still others attribute it t o inorganic catalytic agents. Although much work has been done t o stu-dy the agents which cause t h e fermentation, little has been done t o study in detail the chemical changes which occur. Nom it seems t h a t a more thorough knowledge of the chemical changes which occur should throw some light upon the nature of the agents which produce these changes. AGESTS
PRODUCING
THE
FERXEBTATION
IP; T H E
RE-
SWEATING PROCESS
I. R ~ I C R O o R G A N I S ~ l S - S U C h S ~ a n d Zbelieved t h a t there existed a ferment, t h e action of which was similar t o t h a t of lactic, acetic and butyric acid ferments. Having isolated numerous bacteria from fermenting tobacco, he attributed the fermentation mainly t o bacteria, and thought t h a t if pure cultures could be obtained from Havana tobacco, it would be possible t o produce, in home-grown tobaccos, aromas similar t o those of Havana tobacco. This plan, however, was not a commercial success. Behrens3 isolated a number of organisms from fermenting tobacco, among which were Aspergillus j z m i g a t u s and B a c i l l u s subtilus. He concludes t h a t microorganisms play an important part in fermentation Konig4 isolated D i p l o c o c c u s t a b a c i and B a c i l l u s t a b a c i , which he thought played an important part in fermentation. Nessler, “Gahrung des Tabaks,” De? Tabak, 1867, p. 122, Manheim. Emil Suchslands, “Uber Tabakfermentation,” Be?. d. Bot. GcS.. 9 (1891). 79. 3 J. Behrens, Cenlr. fuer Bakt. und Par., 2, A b l . II, 1896. 4 C. J . Konig, I b i d . , 2, Abl. V I , 1909, pp. 344-355. 1 J.
2
