70 CHEMICAL EXAMINATION 



1000 c.cms. of milk at 60° F. over an equal volume of water at 

 the same temperature. Thus, a Specific Gravity of 1032.2 

 (water = 1000) is usually expressed as 32.2 or, 32.2° lactometer 

 scale. 



Lactometers indicate the specific gravity at a temperature 

 of 60° F. and it is, therefore, necessary to either bring the sample 

 to this temperature or to correct the reading. It is much more 

 convenient to ascertain the temperature of the sample imme- 

 diately before taking the specific gravity and to correct this 

 result to 60° F. by means of Table LXVIII, which will be 

 found in the appendix. 



It is important that the specific gravity of milk should not be 

 determined within a short period of milking as, during the first 

 four hours, there is a decided increase often amounting to 1 to 

 1.5° (Recknagers phenomenon). The gravity should also 

 never be taken immediately after violent agitation of the sample 

 as the air entrapped by the fat globules during such a process 

 may lead to serious errors. If violent agitation is necessary for 

 any purpose, it is advisable to allow the sample to remain quies- 

 cent for two hours before proceeding with the specific gravity 

 determination. No attempt should be made to take the spe- 

 cific gravity of a sample that has commenced to curdle. 



Total Solids, by Calculation. As the fatty and non-fatty 

 portions of milk are comparatively constant in composition, 

 it is evident that the specific gravity of milk can be calculated 

 from the percentages of these constituents. Fat tends to reduce 

 the gravity, and non-fatty solids to increase it. Hehner and 

 Richmond found that the following formula expressed with a 

 fair degree of accuracy the quantitative relation between these 

 constituents: 



F= 0.859 T. S.-'0.21SQG. 



Where F = percentage of fat, T. S. the percentage of total 

 solids and G the specific gravity expressed as mentioned above. 

 From this formula T. >S. = 1.164F+0.2546G. 



A simplified form of this formula that has come into general 



