MILK TESTING. 67 



necessary to form an opinion from single constituent properties of 

 the milk. For this object a number of so-called milk -testing 

 methods of a most varied kind were employed. In this matter 

 practice, more shrewd than theory, adopted the determination of the 

 specific gravity as affording the most valuable test. For a period of 

 ten years the importance of this test was quite undervalued on 

 account of the careless, unscientific method in which some early in- 

 vestigators carried it out, and it has only been re-established by later 

 investigations. Chemists on their side recommended the determin- 

 ation of one or other of the milk constituents, generally the milk- 

 fat, and, in addition to this, quite a number of other tests of milk. 

 Many of these tests were proved to be worthless on account of a 

 want of knowledge of their true significance, as well as because 

 they were often based on false assumptions, due to ignorance of the 

 true composition of milk. Owing to the advance in our knowledge 

 of the nature of milk, made since 1876, the improvement in methods 

 of chemical analysis, and the discovery of Soxhlet's areometric 

 method of determining fat which gives results as reliable as 

 those obtained by gravimetric methods, and dispenses with the 

 use of the chemical balance, while it is simpler and more con- 

 venient to apply, the older methods in use have been replaced, 

 and have now become antiquated; indeed they possess now only 

 historic interest. 



For the purpose of judging milk, it is quite immaterial whether 

 the quantities of nitrogenous matter, milk-sugar, and mineral matter 

 are determined separately, or all together, as " solids not fat ". In 

 the first place, we know too little with regard to the variation which 

 these constituents with perhaps the single exception of the mineral 

 matter are subject to, to form a decisive opinion based on the 

 amount of any one of them. In the second place, the respective 

 ratio of the three constituents is not at all, or very slightly, altered 

 by such adulteration as is commonly met with in practice, so that it 

 may be said to give little assistance to our judgment; and thirdly, 

 in the case of watered milk, the diminution in the quantity of one 

 or other of these constituents furnishes us with no truer indication 

 than the diminution in the total quantity. At present, therefore, a 

 full analysis is seldom made unless we have to do with some 

 particular kind of adulteration. Instead of a full analysis, we 

 generally determine the specific gravity at 15 C. (s), the percentage 

 of fat (/), the percentage of total solids (t), the sum of the three 



