CASEIR I N COWS’ NILK.
635
number, and even s w h material as manufacturer’s catalogues and illustrated price lists will be found to contain information of much value upon subjects relating to the supplies needed in all factories. I n conclusion it may be acknowledged that this plan of instruction is essentially a utilitarian one. This is in accordance with the general drift of the scientific education of to-day. T o use Lord Bacon’s expression the aim is to gather fruit, not flowers. T h e training of the mind will incidentally be one of the results of such a system. But the main object will be the imparting of actual knowledge and the teaching of specific facts. T h e manufacturing chemist who has to meet the difficulties that constantly arise in the practice of his profession is like a nian who is lost in the Alps. What he wants, is not to improve his mind, but to find the way. T h e present system of instruction does not meet the requirements made upon it. It teaches the principles of the science but does not go far enough. As Macaulay said of the ancient philosophers, every trace of intellectual cultivation is there except a harvest. T h e subject of industrial chemistry evidently has not received the attention it deserves in our schools of science. PHILADELPHIA, P A .
THE DETERMINATION OF CASEIN IN COWS’ I1ILK. BY L.L.V A N
SLYKF.. Recei,ed Auyurt 31, 1893.
T
HE methods originally proposed by Hoppe-Seyler and
Ritthausen have been conimonly employed for the separation and determination of casein in cow’s milk. In both methods, the milk is diluted with water and a sinal1 amount of acetic acid is added. T h e precipitation is rendered complete, in one case, by raising the temperature to 40’ C., and, in the other case, by passing a current of carbon dioxide through the niixture at ordinary temperatures. T h e precipitate is filtered, washed first with water, and then with ether to remove fat and is finally dried and weighed on the filter. T h e absence of specific directions touching several steps of the operation led me to investigate some of the conditions pertaining to the deterniination of casein, among which were the following :
636
C A S E I N IT COW'S'
MILK.
Comparison of the two methods. Influence of amount of acid used in precipitating casein. 3. Use of different acids iii precipitating casein. 4. Influence of teiiiperature arid time of digestion on precipitation of casein. 5. T h e precipitation of casein in fresh aiid in old milk. 6. T h e use of preservatives in keeping milk, and influence on the determination of casein. T h e tedious method involved in washing the precipitated casein free from fat by ether and in subsequent drying and weigliiiig on the filter paper was entirely discarded. T h e preo ~ i on the filter t u o cipitated casein was washed bj. d e c a ~ ~ t a t i aiid or three times. T h e filter and contents were then treated b y the ordinary Kjeldahl method for the deterillination of nitrogen, the factor 6 . 2j being used to convert the aniount of iiitrogeii into a n equivalent of casein, when this was desired. This use of the Kjeldahl inetliod i n detemiiniiig the ariiourit oi casein was suggested and employed sometime since by several cheinists ami is 110w very generally used- in the analysis of dairy-products. T h e advantages of its use over the old method i n point of accurac)- anti simplicity are too evident and too well k11o~riito deserve further rilexition. Much credit is due to 11r. -1.I,. Kxiisely ~vliohas done valuable work in carr).ing out the analytical details of the investigation. ( r Com)ari.roii ti'cszclfs Obtai?it,d 41, Pwcipiiofijig C u s ~ i i iin Mil& u f u Temperaficl-c q f q 0 c'. wifhoiif Curboii Dio.n-idt, a7id w i f h Ca rbois Dioxide a t Ordiisa ry 7 ; w p e r af ures.-'She riiethod employed i n making the comparison was, briefly, as follows : About ten grams of milk were used in each case. T h i s amount of riiilk was diluted with mater at 40"-4z' C . to 100 cc. and then 1.5 cc. of a solution containing ten per cent. of acetic acid were added and the solution was carefully stirred \\it11 a glass rod. T h e resulting precipitate was washed tn.0 or three times 13). decantation and 011 the filter ; finally, the filter-paper and contents were digested according to the Kjeldahl niethod for determining nitrogen. 1x1 the other ca,se, the milk was diluted to roo cc. with water of the temperature of the room, then I .5 cc. of the s:iine dilute acetic acid as that employed above were added, I.
2.
637
CASEIN I N COWS' MILK.
after which a stream of carbon dioxide was passed through the solution, until the liquid above the precipitate was clear or very nearly so. T h e subsequent filtration, washing, and determination of nitrogen were made as above. T h e following results were obtained by the two methods with two different samples of milk, triplicate determinations being made in each case : Method B, precipitation with aid of carbon dioxide, sample KO.I.
Method A, precipitation a t 40'C.. sample KO.I .
( a ) 0.475 (b) 0.474 (c) 0.469
--
.. ..per cent. nitrogen .... ....
"
"
' I
"
I'
''
Average 0.473
. ...per cent. nitrogen * . . e
-
Average 0.455
-
Average 0.476
Sample No. 2.
( a ) 0.458 (b) 0.458 (C) 0.449
. .... ....
( a ) 0.486 . ..per cent. nitrogen (b) 0.480 " " ( c ) 0.461 " " '
" "
"
'' ''
Sample NO. 2.
( a ) 0.454 (b)o.w (C) 0.455
--
. . .. per cent. nitrogen .... '' "
....
I'
Average 0.451
Statement of Results.-The above results indicate: First, that essentially the same results are obtained whether we precipitate the casein in cows' milk at a temperature of 40' C. without carbon dioxide, or at ordinary temperatures with the aid of carbon dioxide, other conditions being uniform. In sample No. I , the results differed by 0.003 per cent. of nitrogen ; in sample No. 2 , by 0.004 per cent. of nitrogen, the excess being first with one method and then with the other. Second, that the individual results obtained by several determinations of the same milk agree closely by either method, somewhat closer concordance being given by precipitation at 40' C. Thus, in sample No. I , the greatest difference in three determinations was 0.006 per cent. of nitrogen at 40' C., and 0.025 per cent. nitrogen with the other method. In sample No. 2 , the greatest difference was 0.009 per cent. nitrogen at 40' C. in three determinations, and 0.011 per cent. nitrogen with the other method. (2) lnjuence of Amount of Acid Used i n Precipitating Casein.T h e acid used was a solution containing ten per cent. by weight of acetic acid. This dilute acetic acid was used in amounts
638
CASEIN I N COWS' 3IIT.K
varying from 0.5 to =jcc. T o about ten granis of milk, sufficient water at 40°-4z0 C . was added to dilute to IOO cc. and the acetic acid was then added. The operation was conipleted in the nianner described above. Helow we present the analytical results tabulated : I'er ceitt. of nitroget! .XlllOllllt
of acid iised
r n , j cc.
Sample Yo.
I..
....... /
1.0
2.0
* %
\ 3.0
i 1.0
Sarr1ple s o .
I
2
)
1.5
;
2.0
[ 3.0
cc.
' (
10.5 cc.
\ , Sample S o . 3 . .
1.0
I d
1.5
. . . . . . . iI 2.0 2.5
"
I 3.0 1
4.0
' /
5.0 0.5
Sample No. 4 . . .......
1.0
(1.5
CC.
.. '1
found i n t h e prvcipitate
slightly clouc1y.. . . . . . . . 0 . ~ 5 8 clc.ar . . . . . . . . . . . . . . . . . . . 0.45s clear . . . . . . . . . . . . . . . . . . . 0.519 (! 1eiir ................... 0.441 clear clt.;ir
...................
0,475
................... 0 . 4 7 3 c l e a r . . . . . . . . . . . . . . . . . . 0.469 slightly c l o u d y . . . . . . . . . 0..15~ itiilky .................. 0.1 I j quitc cloudy ............ 0 . 4 ~ 1
................... 0.545 ................... 0.550 . . . . . . . . . . . . . . . . . . . 0.545 . . . . . . . . . . . . . . . . . . .0 . 5 3 ; slightly cloudy . . . . . . . . . O . j r ; tiiilky . . . . . . . . . . . . . . . . . . O . . ; ~ O
clear c 1e:i I' clcnr clear
111ilLy ..................0.059 slightly cloudy ......... 0 . 5 5 1 clear ................... (,.j50
data presented in the preceding table indicate : First, that i n one sample 0 . 5 cc. of acid gave a inaxiniuiii ariiount of nitrogen in the precipitate, while in two other saiiiples, the amount of nitrogen obtained in the precipitate was very low. In each instance where the lowest results were given, the filtrate was milky in appearance. Second, that in three samples out of four, the use of 1.0 cc. of acid gave highest results, the filtrate being clear or only faintly cloudy. Third, that, i n most instances, the use of I . j cc. of acid gave the highest results, with a clear filtrate in every case. Fourth, that the use of two cc. of acid gave very nearly the same results as the use of 1.5 cc. of acid in most cases, the filtrate being clear. Statcii2eiit of
Reszdts.-The
Character of filtratt,
1
Kind of acid used.
Amount of acid used.
1,
1
Character of filtrate.
clear clear
cloudy ~1.0- - _ _ _ _ Acetic acid Hydrochloric
1;
1.5 cc.
a; I'
0.75
clear cloud; cloudy milky
1,
~precipitate, ~&~~~~ionf
Character of precipitate.
flocculent s'exvh't gelatinous
i I
0.465 0,470 0.457
"
flocculent gelatinous
~ ~
0.417 . .
_
_
0.464 0.410 0.404 0.Igg
Stafemenf of Results.-The results contained in the foregoing table show : First, that lactic acid gives results closely agreeing with those obtained by the use of acetic acid, when about one cc. of a ten
_
640
cASP::s
I?;
cows'
31ILK
per cent. solution of lactic acid is used. but if 0.j cc. more or less than one cc. of lactic acid are used, the results are very Ion.. T h e precipitate rvas flocculent and filtered readily. Second. that a ten per cent. solution of sulphuric acid when used to the estent of 0.j cc. for ten grains of milk gave results closely agreeing with those gireii by the use of acetic acid, but that ivlieii iiiore than 0 .j cc. .v\.t.re used. tlie results became lower. T h e filtrate \vas clear, but the casein did not separate i n flocculent condition, liaviiig a teiidciicy to t)econie gelatinous. Several filtrations \Yere required to gct a clear filtrate, and filtratioii \vas slow. Third. that very unsatisfactory results were given by tlie use T h e filtrate of h!.drociiloric acid, whatever the ariiount used \vas cloud!. or milky, tlie precipitate gelatinous, the filtration extreiiiely slmv, and the results I m v . Fourth, for the most satisfactor!- results, for the flocculent c1i:irwtt.r of the precipitate, for rapidit!, of precipitation, filtration, etc., tlit use of acetic acid liatl n great advantage over the other acids tried. ( + 1 l)tflicc)/rc>cf K.r)rl)
