308 MASSACHUSETTS AGRICULTURE. 



Dinacourt's galactometer is also an areometer, but divided 

 into 100 degrees. 100 degrees is equal 1.029 specific gravity, 

 which concentration is assumed to represent that of good milk ; 

 zero indicates pure water. For testing skimmed milk a similar 

 instrument is used upon which 100 degrees refers to a specific 

 gravity of 1.033, the specific gravity of skimmed milk under 

 ordinary circumstances. From the fact that the specific gravity 

 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 preceding mode of 

 examination, optical tests have been proposed. Donne's and 

 Vogel's lactoscope are designed for that purpose, and are based 

 upon the assumption that the more concentrated 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 water, and mixtures of both. Unfor- 

 tunately the fat globules mainly cause the purity of milk to 

 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. Exami- 

 nations with the microscope are very instructive, yet they re- 

 quire the hands of experts. Quite satisfactory results may be 

 obtained by ascertaining 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 wdrds, test the milk in its fresh condition, and 

 again after the cream has been separated 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 observation increases its use- 

 fulness. Whenever time and circumstances permit, it is advis- 

 able to ascertain the specific gravity of the milk, and determine 

 its solid matter by weight, after careful evaporation to dryness. 

 Our exact modes to scientific purposes are unobjectionable, yet 

 they require more time than will usually be allowed for mere 



commercial inquiries. 



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Butter. — Whilst duly recognizing the particular claims of 

 mere practical experience in the successful manufacture of but- 



