i89i.] 253 



a quarter o£ an hour, giving the basin in which they have been placed 

 an occasional shake ; after this pour off the liquid and let the tap run 

 over them for another quarter of an hour or longer. Next pour off 

 the water and do not quite dry the pins, but put them while wet into 

 a round wide mouthed bottle and cover them with a solution of nitric 

 acid, one part of the commercial sort to twelve parts of water, and roll 

 them round the bottle, but not violently. After two or three minutes 

 again drain off the fluid, and cover the pins with the strongest solution 

 of sulphohydrate of ammonium, cork the bottle and allow them to 

 remain for five minutes, gently inverting them for half the time, but 

 not shaking them. The liquor may now be poured off and bottled for 

 future use. Lastly, distribute the pins carefully, for if roughly done 

 their surfaces being yet soft will be scratched, over a paper-covered 

 tray and expose them to the air, and to sunshine if obtainable, until 

 they are thoroughly dry ; if thus left for a few days they will take no 

 harm. They will now be of a rich bronze colour, which will become 

 darker with age. It may here be noted that the addition of half a 

 grain of nitrate of silver to each ounce of the acid bath will yield a 

 much darker colour, while a couple of grains of nitrate of uranium 

 used similarly will give a richer bronze, which will ultimately become 

 darker, though not so dark as that obtained by the nitrate of silver. 



In order to test the resisting powers of all the different kinds of 

 pins, stick examples of each into the cork of a wide mouthed bottle, 

 then put a teaspoonf ul or two of strong acetic or butyric acid into the 

 bottle and replace the cork. In the course of a few hours the vapour 

 of the acids will show up the defects of the tinned and gilt kinds ; 

 the latter will go first, and will be irrorated with a bright green exuda- 

 tion from every porous portion of the coating, and soon afterwards 

 the former will appear to perspire a turquoise greenish-blue liquid 

 from every pore, and the twist of the metal will be made very evident. 

 Then, after thirty-six hours or so it will be found that the enamelling 

 of the black pins has become brittle, and, if the enamel be removed, 

 portions of the metal beneath will be found green. After about the 

 same exposure the bronzed pins will be covered with a greenish bloom, 

 and the surface will be brittle, but, if scratched off, the metal beneath 

 will be found unaffected. The test here given is a much more powerful 

 one than is likely to occur under ordinary entomological circumstances. 



The advantages claimed for pins prepared in the manner suggested 

 are: — that the metal is actually hardened, especially at the points; 

 that the surface is smoother than that of enamel, and that they con- 

 sequently have superior penetrating powers ; that the colour (bronze) 



