FAT IN MILK.

New Zealand Herald, Volume LI, Issue 15496, 1 January 1914, Page 10

FAT IN MILK.

THE GERBEH TEST. USEFUL apparatus. Tins test is csed" extensively in the dairy industry for the estimation of fat m milk, and to the purchaser as well as the pro. ducer it is of inestimable value. To the former it practically warrants his receivin unadulterated milk, while to the latter it is invaluable, in that by keeping milk records and making systematic fat tests ho can eliminate any pout fat-yielding cows, and gradually build up a herd satisfactory both with regard to quality as veil as quantity. Not only does it give an accurate estimation of the fat, but from it, in conjunction with the specific gravity, the total solids, and tin solids other than fat can ba calculated. The tesi invested by a Swiss scientist. Dr. Gerber, is very simple in principle, and can be carried out bv anyone possessing a little skill in manipulation. The estimation depends feolely, as in the case of the separator, on the fact that Use heavier portion of a subsUmce, when subjected to central force, is Ihrom to the outside and the light;: portion to the inside. For this condition to bo brought about the Ma the milk has to be liberated before bang subjected to this centrifugal force. This is accompMfld by adding sulphuric acid, which dissolves all the constituents oj the milk e_-ept the fat, and consequently, the Matter is. £ee. The Apparatus. The necessary apparatus consists of three pipettes, or meausres, with a capacity of 10, 11, and 1 cubic centimetres respectively, a number of Gerber test bottles, a centrifugal fachine, » supply oi sulphuric acid of 1.82 specific gravity, and Borne amyl alcohol, the use of which will be explained later. Where'& considerable number of tests are carried out daiily the pipettes are replaced by automatic mev eures, which measure out the correct amount in the minimum of time, and without the skill required to manipulate a pipette quickly and successfully. _ The best of these measures, to my mind, is the •'tilt," which consists of a glass measuring chamber fixed into the cork, so constructed that on tilting the bottle a chamber holding exactly the requisite amount (lOco or lc.c, as theW maybe) is filled, the (access flowing back into the bottleyleavinz the required amount to be poured down a narrow tube into the test bottle. These mechanical appliances conEi'derably reduce the time taken over the test, besides eliminating any inarcanacy in measuring, and the disastrous results cf obtaining a mouthful of acid. , ;,.- >: : Performing 't_e Test. ,- ;

:t- The 'actual feet is performed as follows : :<4:ioc.c.'o£ the acid is 1 ' measured into the bottle, then lcc of amyl alcohol, and lastly llao of the milk to be tested. This is- therf tightly corked, well shaken up until all the is dissolved, inverted a ifevr tim.».s, placed' in the machine, and spun round for three minutes. This order of placing the liquids in the bottle need not necessarily be adhered to. Frequently ti» milk iei placed in secorJ and- the

alcohol last, although it makes so differ- ; ence to the ultimata result. The acid, however, should always be put in first, as, s Wages' heaviest liquid, ; it sinks to ,the bottom, and i the premature mixing and * heating which -would ! result 'if ■ it ;.were placed in second or last are thus avoided. There is-one decided advantage in placing the alcohol second, in that it acts as a ibaffer be&mnn the milk and the acid and ■.prevents their v coming info, contact until all is tt&Hf. -' - -A. . '•'••:-■' i-The speed at which the bottles are revolved ; ! should be about 1000 revolutions per minute, which, in the casß of the hand machinal, has to ho gauged by'experience.' ■However, on those machines worked by ; ' ■team there • is. an indicator which ; enables the tester to vary the speed to a : nicety. The : ;bottles ■ are placed in the \ machine ivith- the , narrow neck \ towards the centre, consequently during the spinI ning the fat, being by far the lighter por[twis\',oU t'iie mixture, is .thrown towards the centre and rises up the neck of? the fcottle. The percentage of. fat can then ho read off by means of the graduations ©a' the neck of the bottle. To facilitate the "reading, the bottles ; aremade with a flat neck,,' consequently the fat appears as a' J flat column and' is much easier read, also, by, screwing or releasing the cork jth£bottrm:' of the fat column can he ad•justed; to one of the main divisions and is then reaci much, quicker. ■; *-, - :-;'■

' What" to Avoid. I .'• To to* successful in a test there are I ircveral: things to avoid, e.g.,; when put- I Lting:.the liquids in they, should not be | allowed to wet the neck, or tie cork will J not then fit tightly and may.l come out f Cduring the .whirling, with disastrous re- I suits as fa? as the test is cotteemed, and I possibly to oneself as well. * Again, char- i ring ebcraM be avoids. -This is the rea- I con for adding the alcohol, which reduces I charring to & minimum, consequently there 1 should be no chaired matter to interfere H ,-witlt tliii ie?Jii?g. If the; alcohol, how-. 1 ever, is added to the acid" and then left I | for some time it also.begins to char, and | .thus thill mDfifc be avoided. .'; Often in cold 1 •weather on. removing the bottles ■ the fat I 'appears blurred, a.na is not clear enough I ?to read. ,In this case ", the tube ', must "be I I placed in fairly hot'. water for a minute I or two and again whirled. ' This will gene- ; tally nie>jfc the cawi, and a correct reading J will be obtained. • The addition of the I milk requires spec al care. If it is rushed I in anyhow, instead of dropped steadily j down thn side of lie tube, it immediately ] forms a black, charred mess, which may < completely epofl the test, Another fre- i quent cause of an inferior test is spinning [ too long, or riot, long enough. *In the j former case the fat is not clear, and on I the top there will be found a mass of j bubbles, which render accurate reading | impossible. The objection in the latter 1 case is that Home of the fat may not have 1 risen, and when this is suspected the tube 1 wast be immersed in hot water and given I fin additional whirling. It will be noticed I that the top of the fat column is not 1 straight, but craved, and thus a Tather t serious error may arise from reading to S the top of the muniscus, as the curvature i is called, instead of to the bottom, as it I; it usual to do, '~