THE TECHNOLOGIST. [Jan. i, 1865. 



282 ON CHEMISTRY APPLIED TO THE ARTS. 



neutral substance called lactide. This acid, in a free state, has not yet 

 received any important application in art and manufactures, but I have 

 little doubt that it will some day be largely employed, for we have 

 noticed in a former lecture its advantageous use when produced from rye 

 and other amylaceous substances in removing the lime from various 

 skins intended to be tanned or prepared as there described ; and Mr. E. 

 Hunt has used it in the form of sour milk for the conversion of starch 

 into dextrine (see ' Journal of the Society of Arts,' December 23, 1859). 

 I wish now to say a few words on the mineral substances existing in 

 whey, and which play a most important part in milk as a nutritious 

 substance. We are all of us too apt to overlook the importance of the 

 mineral elements in food, and to consider as essential the organic matters 

 only. In milk, however, its alkaline salts, and especially the phosphate 

 of lime, are as essential (as food) as caseine or fatty matters, for if an in. 

 fant requires the lactine to maintain respiration and the heat of the 

 body, the caseine to contribute to the formation of blood, the phosphate 

 of lime is equally essential to the production of bone ; permit me here 

 to state that the practice adopted by some mothers of feeding infants 

 upon amylaceous substances, such as arrowroot, sago, tapioca, &c, in 

 place of milk, is most pernicious, for these contain neither flesh nor 

 bone-forming element, and milk is the only proper food for infants. 



Having now examined the general properties of some of the most im- 

 portant constituents of milk, let us say a few words on that fluid in its 

 integrity. We all know how rapidly milk becomes sour, especially at a 

 temperature of 70° to 90°, and as this is owing, as already explained, to 

 the formation of lactic acid, the best way to preserve milk sweet for 

 domestic purposes is to add to it every day a few grains of carbonate of 

 soda per pint, to keep the milk alkaline. The possibility of preserving 

 milk for a lengthened period has repeatedly occupied the attention of 

 scientific men, as a most important problem to solve for the benefit of 

 persons undergoing long sea-voyages, but up to a recent date with very 

 imperfect success. One of the best plans proposed is to add to milk 

 7 or 8 per cent, of sugar, and evaporate the whole, agitating all the 

 time, to prevent the formation of the skin, and when reduced to one- 

 iifth of its bulk to introduce it into tin cans, which, after being subjected 

 for half an hour to a temperature of 220°, are hermetically sealed. In 

 1855, l'Abbe Moigno drew the attention of the members of the British 

 Association at Glasgow to milk which he stated contained nothing 

 injurious, and which would keep for a long period. This statement has 

 proved correct, for I have here some milk which has been in the hands 

 of the Secretary of this Society since that period, and which, on being 

 opened to-day, was found perfectly sweet. But if l'Abbe Moigno's pro- 

 cess has remained a secret, M. Pasteur has succeeded in effecting the 

 same end, and probably by the same method. Thus he has found that 

 if milk be heated to 212° it will only remain sweet for a few days, if 

 heated to 220° it will remain sweet for several weeks, but if to 250° 



