108 BACTERIOLOGICAL AND ENZYME CHEMISTRY 



carefully brought to this temperature in a constant tempera- 

 ture water-bath. The stopper is inserted, care being taken 

 that no air bubbles are enclosed. The bottle is allowed 

 to cool somewhat and then quickly wiped dry with a soft 

 cloth and immediately weighed. Consecutive weighings in 

 this manner should not differ by more than a miUigram. 



It is probable that the weight of water will not be exactly 

 fifty grams, but the specific gravity of any Uquid can be deter- 

 mined by fiUing the bottle with the hquid in a similar manner, 

 weighing and dividing the weight of water in the bottle into the 

 weight of the hquid. 



In working with solutions of sugar or similar bodies, in 

 order to determine the amount of sugar present from the 

 specific gravity, a factor known as the solution factor is made 

 use of. 



Thus it has been found that ten grams of maltose made up 

 to 100 c.c. at 60° F. has a specific gravity of 1038"5. 



The amount of maltose contained in 100 c.c. of specific 



gravity 1055 will be —— = 14'285 grams. The 



" •' 3-85 



number 3*85 is termed the solution factor for maltose ; dextrin 



has the same factor. 



The specific gravity and, consequently, the solution factor 



are not the same for every carbohydrate, and an allowance 



must be made for this in specific cases. 



(2) Optical Activity. — The subject of optical activity has 

 been already dealt with in a general manner in Chapter IV. 



The polariscope of Fig. 13 is adjusted as follows i : When 

 the apparatus is well illuminated by the sodium flame, the 

 zero position (the starting point of all experiments) must 

 first be found : this is indicated by the two halves of the 



' Based, by permission from Messrs. Baird and Tatlock (London), Ltd., 

 on the instructions issued for use with the Lippioh model half-shadow 

 polariscope. 



