Chapter I : Preparation of Reagents 13 



alcohol if it has not already been prepared. Keep the absolute 

 alcohol and the xylol carefully corked to exclude moisture. 

 Before measuring out any of these reagents, see that both the 

 graduate and bottle are perfectly clean and dry. 



MEMORANDA 



1. Ethyl Alcohol is the kind commonly used in histological labora- 

 tories. Upon presentation of the proper credentials to the internal 

 revenue officers, it may be purchased by the barrel from distillers, tax 

 free, by educational institutions. Such commercial alcohol is of about 

 96 per cent, strength. When the strength is unknown it should be tested 

 by means of an alcoholometer (see 2, below). 



Methyl Alcohol (called also wood alcohol or wood spirits) is cheaper 

 than ethyl alcohol in case the latter cannot" be had tax free, and is fairly 

 satisfactory in most cases. It is poisonous and must be carefully hand- 

 led. It is of about 90 per cent, strength. 



Synthol is a manufactured product now on the market which seems 

 to answer the purposes of ordinary absolute alcohol. It is designated as 

 a synthetic alcohol by its manufacturers and is cheaper than absolute 

 alcohol. 



Rectified Spirit is a 91 per cent, alcohol (84 per cent, in England). 



2. The Alcoholometer is a convenient instrument for determining the 

 strength of alcohol, or the percentage of absolute alcohol in a spirituous 

 mixture. It is a kind of hydrometer with a scale marked to indicate the 

 percentages of alcohol. Different strengths of alcohol have different 

 specific gravities, consequently, the instrument will float higher or lower 

 in the liquid depending upon the percentage of alcohol present. The 

 number on the scale just at the surface of the liquid indicates its strength. 



3. Rule for Dilution of a given strength of a solution with a lower 

 per cent, of the same solution. (For where the diluent is water, i. e., 

 zero per cent., see rule under reagent 1.) Subtract the per cent, required 

 from the per cent, of the solution to be diluted; also subtract the per 

 cent, of the diluent from that of the strength required. The differences 

 are the relative proportions of the diluent and the solution to be diluted 

 that must be used. Thus, to prepare a 35 per cent, solution from 95 and 

 20 per cent, solutions: 95-35 = 60; 35-20 = 15; hence, 60 to 15, or 4 to 

 1 are the proportions desired. That is, 4 parts of the 20 per cent, and 1 

 part of the 95 per cent, solution must be used to obtain a 35 per cent, 

 solution. 



4. " To Remove Fixed Stoppers, take the bottle in the left hand with the 

 forefinger applied to one side of the stopper, then tap the other side of 



