Jan. 1, 1865.1 THE TECHNOLOGIST. 



ON CHEMISTRY APPLIED TO THE ARTS. 283 



(under pressure, of course) the milk will keep for any length of time. 

 This, according to M. Pasteur, is owing to the spores or eggs which 

 generate lactic fermentation being destroyed by the high temperature, 

 and thus the possibility of fermentation is put an end to. The adul- 

 teration of milk by v-arious substances stated to have been discovered 

 therein has, I think, been greatly over-estimated, as I have never 

 found any of them in the samples of milk which I have analysed ; in 

 fact, the most easy and cheapest of all is the addition of water. It is 

 comparatively easy to ascertain if milk has been tampered with ; but, 

 without entering into details of the methods necessary to estimate the 

 exact extent of adulteration, I may mention the following plan : — If a 

 glass tube, divided into 100 equal parts, is filled with milk and left 

 standing for twenty-four hours, the cream will rise to the upper part of 

 the tube, and, if the milk is genuine, will occupy from eleven to thirteen 

 divisions. Another practical method is to add to the milk a little 

 caustic soda, and agitate the whole with a little ether and alcohol, which 

 dissolves the fatty matters ; this etherial solution is removed from the 

 milk and evaporated, when the fatty matters remain, and experience 

 has shown that 1,000 parts of good milk will yield thirty-seven parts of 

 fatty matters. Any milk leaving no more than twenty-seven must 

 have been tampered with. Dr. Voelcker suggests the employment of 

 a hydrometer as a means of ascertaining the quality of milk, as 

 the specific gravity of that fluid is an excellent test. From a great 

 number of experiments he has ascertained that good new milk has a 

 specific gravity of 1*030, whilst if good milk is adulterated with 20 per 

 cent, of water its specific gravity will fall to 1*025. 



Urine is a fluid secreted by the kidneys, which organs separate from 

 the blood as it circulates through them any excess of water it may con- 

 tain, as well as many organic substances which have fulfilled their vital 

 function in the animal economy, and which require to be removed 

 from the system. The composition of urine varies greatly in different 

 individuals, and in the same individual at different times, and is in- 

 fluenced by diet, exercise, state of health, &c, as shown by Dr. Bence 

 Jones and Dr. Edward Smith ; but without detailing these variations, 

 which would occupy far more time than the limits of a lecture would 

 permit, allow me to call your attention to the following table, showing 

 the composition of human and herbivorous animals' urine : — 



Human. 

 Water ..... 933-000 



Urea ..... 30-100 



Lactic acid . . ~) 



Lactate of ammonia | 



Extractive matter . . j 



Kreatin ....)■ 



Kreatinine .... 

 Hippuric acid 



Indican .... 



Colloid acid (W. Marcet) 



