FIXING AND PRESERVATIVE MEDIUMS 31 



Mix thoroughly, and, as heat is evolved by this mixing, let 

 it stand for some hours {i.e. all night) to cool and precipitate. 

 Afterwards filter through ordinary grey filter-paper (preferably 

 doubled), and it will be brilliantly clear and clean, and may 

 then be used. This is the method adopted in the Leicester 

 Museum, and (so far) with the best results as a preservative, but 

 of course it does not preserve the natural colours for any length 

 of time. 



70 per cent. Alcohol. — This is, as will be seen by Mr. Lee's 

 most useful table, made by taking 100 volumes of 90 per cent, 

 alcohol or methyl-alcohol and 3 1 volumes of water ; but Ball's 

 method for getting a 70 per cent, alcohol in a rough-and- 

 ready manner is as follows : ^ — " The 70 per cent, alcohol is 

 readily made with a sufficient approximation to accuracy by 

 remembering that by adding nearly four-tenths of its volume 

 of water to the ordinary 95 to 97 per cent, alcohol of com- 

 merce, an alcohol percentage of 70 is reached. Thus with 

 an ordinary foot-rule the operator can mix his alcohols in 

 cylindrical jars, thus : — 



" Stand the jar upon the table, place the rule by the side of 

 it with the scale next the glass, then pour in alcohol till some 

 arbitrarily chosen tenth division of the rule outside is reached 

 by the surface of the spirit, then add water to the spirit to the 

 amount of nearly four more similar divisions of the rule, when 

 the requisite dilution of 70 per cent, approximately is reached." 



At Naples, as now in many other museums, 70 per cent, 

 alcohol is the strength commonly used for definitive preservation 

 of most organisms, and ordinary alcohol may, even if it has 

 been used and become charged with organic matter thereby, 

 be redistilled and neutralised by the addition of lime should it 

 prove acid, or of hydrochloric acid should it, on the other hand, 

 be alkaline. 



' Instriuiions for collecting Molbisks, etc., 1892, pp. 44, 45, Rep. Smithsonian Inst. 



