330 



THE COMPOSITION OF MILK PRODUCTS. 



cally always absent from condensed milk sold in small tins, but 

 in slightly sweetened condensed milk containing less than 3 per 

 cent, of cane sugar Monier-Williams found 0-66 to 0-88 per cent, 

 of boric acid. 



Composition of Unsweetened Milk. Unsweetened con- 

 densed milks are prepared in a similar manner, except that the 

 addition of sugar is omitted. 



The composition of this product is shown by the following 

 analyses (Table XCL) : 



TABLE XCI. COMPOSITION OF UNSWEETENED MILK. 



These milks have all been sterilised by heat. They have the 

 analytical characters of sterilised milk. 



Unsterilised condensed milk is also an article of commerce ; 

 Pearmain and Moor have found boric acid in a preparation of 

 this kind, which was sold for diluting and mixing with whole 

 milk. 



It is noticed that the totals of analyses of condensed milk 

 almost invariably add up distinctly below 100 per cent. ; it is 

 probable that the milk-sugar is underestimated. In condensed 

 milk the layer of solution which is attracted round the fat globules 

 by surface energy has probably a composition which is identical 

 with the composition of the liquid in which the globules are 

 suspended. When condensed milk is diluted with water it is 

 doubtful whether the liquid in this layer is diluted by the water, 

 as it is held by a great force, and acts as though separated by 

 a semi-permeable membrane, through which the dissolved 

 solids must pass by osmose. As the milk is usually diluted 

 with cold water, this process of osmose takes a considerable 

 time, and the whole of the milk-sugar is not obtained in solution, 

 but a portion is taken down by the fat globules, when they are 

 removed previous to the estimation of the milk-sugar. The 

 same cause can be assigned to the fact that the fat globules in 

 diluted condensed milk rise with such extreme slowness ; a dense 

 layer round the globules increases its mean density, and makes 

 this approach nearly the density of the serum. 



