HOW TO COLLECT DIPTERA (TWO-WINGED FLIES). 61 
One or two cyanide killing -bottles, not too large to be carried in the 
pocket when required; or a larger-sized cyanide killing-jar, or 
materials for making same, as follows : | lb. of cyanide of potassium,* 
1 lb. of plaster of P^iris, a glass jar with wide mouth and closely 
fitting lid.f 
a second (and if necessary a third) coat of paint being added after the first is 
dry. Any paint or glue on the glass can be removed with a penknife ; if the 
jaconet protrudes too far over the glass, cut it round with a penknife and 
remove it. (Glass-bottomed boxes already protected in this manner can be 
obtained from Miss E. M. Bowdler Sharpe, Entomological Agency, 345, Fulbam 
Road, London, S.W.) 
A simpler method of protecting the boxes is to coat them (especially the 
joints) with shellac dissolved in absolute alcohol. 
Glass-bottomed boxes of this kind constructed of tin are sometimes sold : but 
these are not to be recommended, since when in use in warm climates they are 
apt to become very hot, with the result that flies contained in them are killed 
and become dry prematurely. 
* If it is intended to take cyanide to a damp tropical climate, it should be 
conveyed in the form of lumps, in a bottle with a tightly fitting glass stopper. 
Cyanide of potassium is also sold in rods, and, in this form, might be con- 
veniently carried in short lengths in hermetically sealed tubes of thin glass 
and diameter and length just sufficient to take the section of cyanide rod. 
f Cyanide killing-bottles can be procured ready for use from Hinton & Co., 
Bedford Street, London, W.C., or any other chemist will prepare one to order; 
but when Diptera are collected in the manner advised below, it is preferable to 
use a large-sized killing-jar, which should be made as follows : — Take any 
fairly large glass jar (such as a pickle-bottle) with a wide mouth and closely 
fitting lid (a lever-lid such as those often fitted to pickle-bottles would answer 
admirably), and cover the bottom with a layer of dry plaster of Paris to the 
depth of \ inch ; pour in above this a layer equal in depth consisting of 
jwwdered cyanide of potassium, mixed with rather more than its bulk 
of dry plaster of Paris ; cover this mixture with a layer of dry plaster of 
Paris to the depth of \ inch or so ; and pour in above the whole a lajer 
\ inch in depth, consisting of plaster of Paris mixed with water to the con- 
sistency of cream. As soon as the top layer of plaster is dry the jar is ready 
for use : the plaster, however, should be covered with several thicknesses of 
blotting-paper, to avoid risk of injury to specimens in case the surface should 
at any time become wet. To obviate the danger of cracking the jar owing to 
the heat evolved when plaster of Paris is mixed with water, it maybe advisable 
co stand the jar in warm water before adding the final layer. The exact 
amount of cyanide of potassium to be used is of no great consequence ; but in 
