348 



REAGENTS AND THEIR PREPARATION 



[Ch. X 



even will not give an exact mixture of alcohol, for a mixture of alcohol 

 and water diminishes somewhat in volume. To get true percentages 

 an alcoholometer for testing the specific gravity is used. 



A simple method of getting approximately correct mixtures of 

 alcohol is the following: Pour the strong alcohol into a graduate 

 glass (fig. 209AB) until the volume is the same as the desired per- 

 centage; then add water until 

 the volume is the same as the 

 original percentage of the alco- 

 hol. Example: To get 50 % from 

 95 % alcohol put 50 cc. of 95 % 

 into a graduate and fill the grad- 

 uate to 95 cc. with water, and 

 the resulting mixture will be 

 50% alcohol, and so with all 

 other strengths. Here the 

 shrinkage is eliminated from 

 consideration, because the water 

 and alcohol are not measured 

 separately and then mixed, but 

 one is added to the other until 

 a given volume is attained. 



Fig. 



B 



209. Glass Graduates for 

 Measuring Liquids. 



A Graduate with sloping sides for 

 large quantities. 



B Graduate with straight sides for 

 smaller quantities and more accurate de- 

 termination. 



Preparation of Reagents 



§ 539. Albumen fixative 



(Mayer's). — This consists of 

 equal parts of well-beaten white of egg and glycerin. To each 50 cc. 

 of this 1 gram of salicylate of soda is added to prevent putrefactive 

 changes. This must be carefully filtered. For method of use see 

 Ch. XL 



§ 540. Alcohol (ethyl), C 2 H 5 OH. — Ethyl or grain alcohol is mostly 

 used for histologic purposes. (A) Absolute alcohol (i.e., alcohol 

 of 99%) is recommended for many purposes, but if plenty of 

 95% alcohol is used it answers every purpose in histology, in a dry 

 climate or in a warm, dry room. When it is damp, dehydration is 

 greatly facilitated by the use of absolute alcohol. 



