﻿184 THE ENTOMOLOGIST. 



would suppose unstable and delicate — insect colours; neither 

 would he be prepared for the dolorous monotony in the 

 changes produced by most dissimilar reagents, — when they 

 have any effect at all. At starting, I divided my reagents 

 into several different classes, viz., " mineral acids, organic 

 acids, alkalis, various salts, and various organic reagents," the 

 last two classes being of a somewhat heterogeneous character. 

 This division turns out to be all nonsense : there are (so far as 

 my experience goes) only two classes of reagents, viz., those that 

 destroy or alter the colours, and those that have little or no 

 effect; and the majority belong to the latter class. I had started 

 off with great enthusiasm, experimenting with about two dozen 

 different reagents, and tabulating my results on separate sheets, 

 drawn up for " mineral acid " reagents, " alkalis," &c, respectively ; 

 but, wise from experience, I propose in future to work with only 

 half a dozen reagents, such as have proved serviceable already. 



I will now give a list of the various reagents that have been 

 tested, first making one or two preliminary explanations for the 

 benefit of any non-chemical readers who may possibly not under- 

 stand entirely some of the expressions used. The acids (and 

 ammonia) described as " strong," are such as are customarily 

 supplied for laboratory use ; a 50 per cent, acid, is one of these 

 diluted with its own bulk of water, and so on; a 50, 25, 10 per 

 cent, solution of any salt, &c, implies that 100 cubic centimetres 

 of the solution contain 50, 25, 10 grammes of the salt.* (In the 

 case of the caustic hydrate solutions used, this is not strictly 

 accurate, since in making up these the ordinary " stick " caustic 

 was employed, and this contains a percentage of water. This 

 fact is, however, of no importance, so long as uniform solutions 

 are always used.) Many acids are solid at the ordinary tempera- 

 tures, and therefore they were dissolved in water, like salts, and 

 made up to various per cent solutions. In some instances, 

 saturated solutions were made; that is, of course, as much was 

 dissolved as the water could take up. In only two or three cases, 

 by careless oversight, were my reagents un quantitative ; but, except 

 in one instance, such reagents were, fortunately, unimportant. 

 All the solutions are aqueous, unless expressly stated otherwise. 



I. f Sulphuric acid 40 per cent. (?) 



Nitric acid 50 per cent. 



I Hydrochloric acid Strong. 



Hydriodic acid Solution of S. G., 1'500. 



Phosphoric acid 25 per cent. 



Hydrofluosilicic acid The usual analytical solution. 



Boric acid Saturated alcoholic solution. 



* In the metric system, 1 gramme is the weight of one cubic centimetre of dis- 

 tilled water at standard temperature and pressure. 



t I very stupidly omitted to note the strength of this reagent. 

 J Popularly known as muriatic acid. 



