38 
LABORATORY MANUAL 
EXERCISE NO. 29 
Object: To become acquainted with the use oj the Quevene lactometer for deter¬ 
mining the specific gravity, the solids not fat, the total solids, and 
the specific gravity of total solids of milk. 
Procedure: The normal specific gravity of cow’s milk varies from 1.029- 
1.035 at 60° F., the average being about 1.032. The solids no 
fat (S N F) range slightly above 8.5%, and the total solids 
(T S) is equivalent to the S N F p ] us the fat. The specific 
gravity of T S varies from 1.25-1.34, usually averaging above 
1.30. The addition of a foreign substance or the removal of a 
constituent of milk will usually effect one or more of the above 
constituents, hence a knowledge of lactometer work aids in the 
detection of adulterations. 
A. Mix a sample of milk thoroughly and obtain a 17.6 cc. sample 
for a fat determination. Fill the glass lactometer cylinder 
with milk and insert the lactometer. Allow the lactometer to 
come to rest and read the temperature. If it is above 70° F. 
or below 50° F. cool or warm the sample as necessary. If the 
temperature is within the range given, read the point on the 
lactometer scale to which it has sunken. 
B. Make temperature corrections (F. & W. If 111, 112, 113). 
C. Make calculations necessary to fill in data required under ob¬ 
servations. 
Note: See F. & W. If 118 for cleaning lactometer, and be 
sure the lactometer is dry before it is inserted in the milk. 
Observations: 
Sam¬ 
ple 
% 
fat 
Lact. 
reading 
Temper¬ 
ature 
Corrected 
reading 
% 
SNF 
% 
TS 
Sp. gr. 
of milk 
Sp. gr. 
of solids 
1 
2 
Conclusions: 
Questions: (1) Why is it not possible to obtain the specific gravity of 
milk immediately after milking? 
(2) Why should the lactometer reading be taken immediately after 
the milk is mixed and the lactometer inserted? 
(3) How should the lactometer be read with reference to the 
meniscus? 
(4) Give the formulae for determining the SNF, TS, and the spe¬ 
cific gravity of TS. 
References: F. & W. If 109-121, inclusive, 125; Van S. pp. 175-196; Jud. 
pp. 91-101; St. pp. 136-143. 
