37 



upon which 100 degrees refei's to a specific gravity of 1.033, the 

 specific gravity of skimmed milk under ordinary circumstances. 

 From the fact that the specific gi-avity of good milk, after being 

 raised by skimming, may be restored by the addition of a certain 

 amount of water, it is obvious that the principle which underlies the 

 application of hydrometers is here of little value. To supplement 

 the preceeding mode of examination, optical tests have been pro- 

 posed. Donne's and Vogel's lactoscope are designed for that jnir- 

 pose ; and are based upon the assiunption that the more concen- 

 trated a milk is the thinner the stratum through which light will 

 pass. A scale is connected with the instrument to determine the 

 difference between good milk, and watei% and mixtures of both. 

 Unfortunately the fat gobules which mainly cause the purity of milk 

 vary in percentage, even in a pure article, so much that very little 

 information can be deduced from these indications beyond the 

 question concerning the amount of butter present. Examinations 

 \\ith the microscope are very instructive, yet they require the hands 

 of expei'ts. Quite satisfactory results may be obtained by first ascer- 

 taining the specific gravity of milk, and the subsequent measuring 

 of the amount of cream which separates from a given quantity of it 

 at a certain temperature in a given time ; in other words, test the 

 milk in its fresh condition, and again after the cream has been sepa- 

 rated by means of any good areometer, and notice the amount of 

 cream that has been formed. Proskauer's areometer is constructed 

 with regard to these points ; a scale based on actual obseiwation 

 increases its usefulness Whenever time and circumstances permit, 

 it is advisable to ascertain the specific gravity of the milk, and deter- 

 mine its solid matter by weight, after careful evaporation to diy- 

 ness. Our exact modes for scientific purposes are unobjection- 

 able, yet they require more time than will usually be allowed for 

 mere commercial inquiries. 



BUTTER. 



Whilst duly recognizing the particular claims of mere practical 

 experience in the successful manufacture of butter, I do not hesi- 

 tate to express the behef, that a more careful attention to the chem- 

 istry involved in that operation will eventually give to the practical 

 dairyman a better understanding of the many difiiculties which not 

 unfrequently surround him in his pursuit. 



Milk begins to change dii-ectly after its removal from the 



