APPENDIX. 



885. The Usual Alcohols. The following, or a similarly 

 spaced series of alcohols, should be kept on the table. 



Absolute Alcohol See 101. The so-called "absolute 

 alcohol " of commerce is generally of about 98 per cent, 

 strength. This grade is convenient, but not necessary for 

 ordinary work. Water in alcohol may be detected (YvoN, 

 Comptes Rend., cxxv, 1897, p. 1181) by adding a little 

 coai-sely powdered carbide of calcium ; the merest trace of 

 water causes a disengagement of acetylene gas, and on 

 agitation the alcohol becomes turbid with calcium hydrate. 



95 per cent. Alcohol. This is the average strength of the 

 common strong commercial alcohol, which ranges in general 

 from 94 per cent, to 96 per cent, according to temperature. 

 The strength of this, or of the following, should be deter- 

 mined by means of an areometer (Gay Lussac's being very 

 convenient), so as to form a starting-point for the following- 

 mixtures, which may be made by means of the table, next . 

 This is the usual grade for dehydrating before clearing. It 

 is the highest grade that should be used for dehydrating 

 celloidiii sections. 



90 per cent. Alcohol. May be made by taking 100 vols. 

 95 per cent, alcohol and 5'5 vols. water. Oil of bergamot 

 will clear from this grade. This is the usual strength of the 

 strongest commercial methylated spirit, which, if free from 

 mineral naphtha, is used by some persons instead of pure 

 alcohol. A writer in the Athenaeum, June 4th, 1898, p. 728, 

 says, " We believe that all ordinary methylated spii'it 



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