Page:Pure milk - a lecture delivered in the lecture room of the exhibition, July 30th, 1884 (IA b28525140).pdf/15

 capable of easy digestion, in fact so that the stomach can easily assimilate them. This water is the bone of contention between public analysts and milkmen, and nothing was more common three or four years ago than to hear a long cross-examination directed solely to the elucidation of the very knotty point—as to whether there was any difference between the water natural to milk, which in fact the cow put into it, and the water which the milkman added.

I should like to consider next, by the aid of a set of samples which have been lent me by the Aylesbury Dairy Company, the mode in which the milk is divided by the dairymen into the different articles of commerce which are most frequently made from it. The samples to some extent speak for themselves, and certainly as regards the first series, that of whole milk, I need not detain you any longer, except to say that here we have fat, caseine, and sugar, all shown in the same form as in the larger bottles on the table. Our next two series of samples here show us the division of the whole milk into cream and skim milk. Cream, as I took occasion to tell you some time ago, does not consist entirely of butter fat, but contains fifty to sixty-five per cent., more or less, according to its quality. And in this series of samples we have the cream divided into the constituents present in a good ordinary commercial sample, and you will see that some thirty per cent, of water is still present, and that this water carries with it caseine, albumen, and salts. We may in fact put it another way, and say that, separate any particular constituent of the milk as carefully as possible by mechanical means, and we always find that some small proportion of the other constituents are present; thus, referring to skim milk: in the first separation we find that it still contains some fat; the amount in skim milk is extremely variable, according to the mode of manufacture. The Centrifugal machine, which you can see at work in the south gallery, is by far the most efficient and most successful for separating the cream from the milk.

The principle of the centrifugal separator is practically