282 Dr. Lyon Playfair on the Milk of the Cow. 



ment of the abstract science. Many difficulties occur in the 

 pursuits of a dairy farmer, which render his occupation pre- 

 carious. Such difficulties arise entirely from an ignorance of 

 the scientific relations of the practice in which he is engaged. 

 I have endeavoured in the following paper to point out the 

 causes which so often effect changes in the nature of his pro- 

 duce. 



Boussingault and Lebel* instituted some experiments, with 

 the view of proving that the composition of milk remains 

 constant, when the food given to the cow contains the same 

 amount of nitrogen : and their analyses established this fact, 

 as far as regarded the casein in the milk ; although its other 

 ingredients varied very considerably, according to the nature 

 of the food. The mean of eight analyses described in the 

 first part of their memoir, gives the following composition for 

 the milk of a cow : — 



Casein 3'2 



Butter 4*1 



Sugar 5'1 



Ashes 0-2 



Water 87*4. 



The method employed by these chemists in their analyses 

 did not differ from that used by Peligot in his examination 

 of the milk of the assf. 



It consisted in treating the solid residue of a known weight 

 of milk with aether, and afterwards with water. The loss in 

 weight, after washing with aether, was estimated as butter, 

 while that experienced by a similar treatment with water in- 

 dicated the quantity of sugar; the dried insoluble residue 

 being casein. The latter was incinerated, in order to obtain 

 the ashes of the milk. 



There is an error in this method of analysis, which seems 

 to have escaped the attention of Boussingault and Lebel. It 

 consists in the neglect of the inorganic matters dissolved by 

 the water. In washing with water the mixture of casein and 

 sugar, all the soluble salts of the milk are dissolved. The 

 insoluble salts remain in the residual casein, and these alone 

 were obtained by its incineration, whilst those dissolved by 

 the water were neglected. Consequently, in the analyses of 

 Boussingault, the quantity of sugar in the milk is always too 

 high, and that of the inorganic ingredients too low. 



The method of analysis employed in this paper was, with 

 a few modifications, the same as the above. A weighed por- 

 tion of milk, to which a few drops of acetic acid had pre- 

 viously been added, was evaporated to dryness at the heat of 



* Ann. de Chim. et de Phys. lxxi. 65. f Ibid. lxii. 432. 



