498 APPENDIX. 



dealt with by retailers now contains, by law, at least % per 

 cent, of petroleum, and that methylated spirit free from it 

 can only be obtained by taking special measures." If this 

 be so, I should say it ought not to be used at all. If 

 naphtha be present in alcohol it will become turbid on addi- 

 tion of water. 



85 per cent. Alcohol. Rectified spirit, B. P., is a little 

 weaker than this, viz. 84*5 per cent. 



70 per cent. Alcohol. Only exceptionally powerful clearers, 

 such as anilin oil, will clear from this grade: see 121. 

 This is the proper grade for the temporary preservation of 

 tissues intended for histological study (but see the remarks 

 on preservation on page 5) ; higher grades are best not taken 

 unless it is desired to harden. This is the proper grade for 

 washing out borax-carmine stains, sublimate after fixing, etc. 



50 per cent. Alcohol. This is the strength of proof spirit. 



" One-third Alcohol." See 100. 



886. Table for diluting Alcohol (after GAY-LUSSAC). To use 

 this table, find in the upper horizontal row of figures the 

 percentage of the alcohol that it is desired to dilute, and in 

 the vertical row to the left the percentage of the alcohol it 

 is desired to arrive at. Then follow out the vertical and 

 horizontal rows headed respectively by these figures, and the 

 figure printed at the point of intersection of the two rows will 

 show how many volumes of water must be taken to reduce 

 one hundred volumes of the original alcohol to the required 

 grade. Thus, if it be required to manufacture some 70 per 

 cent, alcohol, starting with 90 per cent., we find the figure 

 90 in the upper column, the figure 70 in the vertical column, 

 and- at the point of intersection we read 31*05, showing that 

 a fraction more than 31 volumes of water must be added to 

 100 volumes of 90 per cent, alcohol. Or similarly, if we 

 wish as before to make 70 per cent, alcohol, but start with 

 an alcohol of 85 per cent., we find that 23*14 volumes of 

 water must be employed. 



