116 



A NA TOMICA L TECHNOL OGY. 



tliat the per cent, of the mixture shall be 50 ; 50 30 = 20 ; 75 50 = 25. The recipro- 

 cals are ^ and ^ s ; reduced to a common denominator, these fractions become T {j ff and 

 T ^, consequently 5 volumes of 30 per cent, alcohol are to be added to 4 volumes of 75 

 per cent, in order that the per cent, of the mixture may be 50. Upon the alcoometer the 

 per cent, is about 52. 



Owing to the unequal specific gravities of alcohol and water, and the contraction which 

 occurs when they are mixed, the results obtained by this method are only approximate, as 

 indicated by the alcoometer. They are, however, sufficiently close for most purposes. 



When liquids of different specific gravities are mixed, they should be thoroughly 

 shaken together before testing with the alcoometer. 



272. Determining the Ratio by Experiment. When a given 

 volume of alcohol is to be made either stronger or weaker, the end 

 may be reached experimentally in either of two ways : The entire 

 volume of the alcohol to be changed may be placed in a jar, and 

 the modifying liquid whether water or weaker or stronger alcohol- 

 may then be introduced gradually until the desired per cent, is 

 attained ; or a given volume of the alcohol to be changed may be 

 placed in the hydrometer jar, and given volumes of the other liquid 

 induced. Having ascertained the ratios, larger volumes may be 

 mixed accordingly. 



In both these cases, the two liquids must be thoroughly shaken 

 or stirred together before testing. 



273. Reduction of 95 per cent. Alcohol by the Addition of 

 Water. Since this is the change most frequently made, we have 

 ascertained by the alcoometer the results of the mixture of water 

 and alcohol in various simple ratios. These ratios are given in the 

 following Table : 



274. Water to be Mixed with Alcohol. If the mixture is for the hardening or storage 

 of specimens, any clean water will answer. But if for the exhibition of finished prepara- 

 tions, the water should be either distilled, or rain water filtered ; otherwise the mixture is 

 liable to be clouded. 



