CHAPTER I 

 PREPARATION OF REAGENTS 



The following reagents should be prepared by each student. 



1. Grades of Alcohol. To obtain a given per cent, of alcohol 

 through dilution of a higher per cent, with distilled water, sub- 

 tract the per cent, required from the per cent, of the alcohol to 

 be diluted ; the difference is the proportion of water that must be 

 added. Thus, if 35 is the per cent, required, and 95 the per cent, 

 to be diluted, then 95 35=60; hence, 60 parts of water and 35 

 parts of 95 per cent, alcohol are the proportions for mixing. 



This means that in practice one needs only to fill the graduated 

 measuring cylinder to the same number as the per cent, required 

 (e. g., 35) with the alcohol to be diluted (e. g., 95) and then fill 

 up to the per cent, of the latter with distilled water. In this way 

 one would obtain 95 c.c. of alcohol of the per cent, required, if 

 the measuring cylinder is graduated in cubic centimeters. 



Prepare about 250 c.c. of 35, 50, 70, and 83 per cent, 'alcohols 

 respectively, from 95 per cent, alcohol and distilled water. The 

 commercial alcohol used, though really about 96 per cent., may 

 be figured on the basis of 95 per cent. 



Owing to the differences in the specific gravities of the differ- 

 ent percentages of alcohol, the above method gives only approxi- 

 mate results; they are sufficiently accurate, however, for most 

 biological work. 



2. Absolute Alcohol. It is customary in most laboratories to 

 purchase so-called absolute alcohol specially prepared for labora- 

 tory purposes. Squibb's absolute alcohol (99.8 per cent.) is 

 commonly used. Inasmuch as such alcohol is an expensive 

 reagent, economy sometimes necessitates that the student under- 

 take the more tedious process of making his own absolute alcohol. 

 Crystals of copper sulphate are heated until the water of crystal- 

 lization is driven off and the sulphate is left as a white powder. 

 Such anhydrous sulphate is added to a bottle of commercial 



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