SPECIFIC GRAVITY. 61 



further expansion or contraction takes place, the water should be 

 adjusted to the line on the wider capillary by the cautious appli- 

 cation of a piece of blotting-paper to the end of the narrow 

 capillary ; the tube is then wiped dry and weighed. The difier- 

 ence in the two weights gives the weight of the water contained 

 in it. The tube is then filled with milk and immersed in water 

 at 15-55° C. (60° F.), and the milk similarly adjusted to the line ; 

 the weight of milk divided by the weight of water gives the 



15 "55° 

 specific gravity of the milk at t^t^fo- 



A specific gravity bottle is used in a similar manner ; the liquid, 

 after inserting the stopper and immersing the bottle in water at 

 15'55°, is adjusted to the line by drawing out the excess with a 

 very fine tube. 



A Sprengel tube of 10 to 20 c.c. capacity is the most suitable 

 size ; it is a disadvantage to use a larger one, as the time taken 

 for the milk to assume the temperature of the suiTOunding water 

 is so much increased that there is danger of a portion of the 

 cream separating. 



The advantages of a Sprengel tube over a specific gravity 

 bottle are : — 



(1) Greater surface for a given volume ; and therefoic the 

 temperature is adjusted quicker. 



(2) There is no stopper to fit ; consequently, no error can be 

 due to difference of position owing to inaccuracy of fit. 



The Westphal balance (Fig. 3) consists of a balance of the 

 " steel-yard " type, carrying a glass plummet at one end ; it is 

 so adjusted that the pointer is at zero when the plummet hangs 

 in air, and is provided with a weight, which, when hooked on to 

 the end, causes the pointer to be at zero when the plummet is 

 immersed in water at 15-55° C. The beam is divided into ten 

 parts, each indicated by a notch, and riders weighing the same, 

 ,V, -tU, and To'oo oi the weight are provided. 



To take the specific gravity, the plummet is immersed m milk 

 at 15-55°, and riders are placed on the notches of the beam till 

 the pointer is at zero. If the y\f rider is on notch 3, the specific 

 .■nivity is 1-03 ; if, in addition, the ,- ^^j rider has to be placed on 

 notch'--*, the specific gravity is 1-03-J; and if, in addition, the 

 - --i^„ rider has to be placed on notch -4 the specific gravity is 

 i'us'-Jl. If a rider is already on a notch, and it is desired to 

 place another thereon, it may be hung on the turned up end of 

 the rider alread\- in position. 



A rule may "be given as follows :— Count 1 for the weight 

 hung on the end, the first decimal from the notch on which the 

 i rider is hung, the second decimal from the notch on which 



