MANUAL OF GENEBAL AGBICULTURE. 99 



neck of a cream bottle that measures fifty per cent fat will 

 hold 10 c.c. or 135.5 grams of mercury. 



(c) Pipette and Acid Cylinder. In calibrating the 

 pipette sufficiently accurate results may be obtained by 

 weighing the quantity of water which the pipette will de- 

 liver, viz., 17.5 grams. A measureful of water may be 

 emptied into a small vessel, weighed, and this vessel 

 weighed a second time. The weight of the water con- 

 tained in the pipette is the difference. 



Calibration of the acid cylinder is not necessary since 

 small variation in the amount of acid measured out does 

 not affect the accuracy of the test. In calibrating any of 

 the glassware water instead of mercury may be used, but 

 is less satisfactory and not in such general use. 



74. DETERMINATION OF THE STRENGTH OR SPE- 

 CIFIC GRAVITY OF SULPHURIC ACID. 



Materials: Milk test bottle, scales, sulphuric acid to 

 be used in the Babcock test, acid hydrometer (See b.) 



(a) Weigh a dry test bottle and then fill with acid 

 exactly to the zero mark. Weigh again accurately and 

 the difference between the two weights will give the 

 weight of the acid. Empty the bottle and thoroughly 

 rinse with water. Wipe the outside dry. Fill with water 

 to the zero mark as before and weigh. The difference be- 

 tween this weight and that of the empty bottle gives the 

 weight of the water. Calculate the specific gravity by 

 dividing the weight of the acid by the weight of the 

 water. If the quotient is between 1.82 and 1.83 the acid 

 is of correct strength. 



If the acid is a little too strong, later in making tests 

 take less than the required amount, perhaps, about 16 c.c. 

 If too weak add a litle more than 17.5 c.c. If the acid 

 is too strong the better way to do is to pour the acid into 

 a bottle containing a small quantity of water. Never 

 dilute sulphuric acid by pouring water into the acid as 

 the acid may be spattered. For more accurate results the 

 temperature of the acid should be 60F. 



