10 Neurological Technique 



For convenience in reducing the stock alcohol to the lower 

 grades required, the following formula has been devised : 

 Let a = the per cent, of the alcohol to be reduced, 

 b = the per cent, of the alcohol required, and 



X = the number of parts of distilled water to be added to loo parts 

 of the alcohol to be reduced, in order to obtain the required per cent. 



a b looa — loob 

 Then , — = , orji; = • 



IOC + X IOC t> 



For example, suppose the stock alcohol to be reduced is 95 

 per cent, and 70 per cent, alcohol is required, then substitut- 

 ing: 



100 X 05 — 100 X 70 2500 



^ = . ^ = ^—=35-7 • 



70 70 



Then 35.7 parts of water added to 100 parts of 95 per cent, 

 alcohol will give 135.7 parts of 70 per cent, alcohol. 



This formula does not give the exact volume percentages, 

 since it does not take into account the physical action between 

 the alcohol and water, and the consequent contraction in volume. 

 To do this the more complex interpolation formula would be 

 required. However, results amply exact for histological pur- 

 poses are given by the above formula. It may be applied for 

 the reduction of any grade of alcohol. 



Commercial alcohol is usually about 95 per cent. Substitut- 

 ing 95 per cent, for a and applying the formula for the grades of 

 alcohol ordinarily required, the following table has been 

 derived : 



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