220 



[see this Review, Ser. B, ii, p. 181] on the effect of the addition of 

 various substances to the dip on its relative content of arsenite and 

 arsenate. Several different sodium arsenites are known, including 

 acid sodium arsenite (NaoO„As.^O./2HO), prepared by dissolving 

 arsenions oxide in a solution of sodium hydrate or sodium carbonate, 

 and evaporating the solution, which contains 80 "2 per cent, of arsenious 

 oxide; sodium metarsenite (Na^OAs^Os or NaAsO.,), formed by 

 boiling the previous compound for some time with sodium carbonate, 

 and washing the residual salt with alcohol; this contains 76-2 per 

 cent, of arsenious oxide; sodium pjTO-arsenite (Nao02As^0.) is 

 produced when sodinm carbonate is fused with an excess of arsenious 

 oxide and theoretically should contain 86 "5 per cent, of arsenious oxide. 

 The commercial arsenite of soda recommended by Watkhis-Pitchford 

 in the " Laboratory " formula is stipulated to contain 80 per cent, of 

 arsenious oxide, and the brands sold in South Africa are usually 

 guaranteed to come up to that standard. These commercial varieties 

 probably contain a mixture of the above-mentioned sodium arsenites 

 in varving proportions. A large number of samples of arsenite of 

 soda have been analysed in the laboratory at Cedara during the past 

 few years, and the arsenic content has ranged from 50 "7 per cent, to 

 82*6 per cent. Some arsenic oxide (As.^O,) is also invariably present, 

 but the amount is generally comparatively small. Seeing, therefore, 

 that the composition of the substances sold as arsenite of soda is so 

 variable, a purchaser should insist on a warranty being submitted 

 with each consignment, and should also send a representative sample 

 to an independent analyst for analysis. The dip fluid in the tank 

 should be submitted for analysis immediately it is made up, before 

 any stock is put through and also at frequent intervals afterwards. 

 The need for this is advocated for the following reasons : — The varying 

 composition of the arsenite of soda employed ; the serious errors 

 that are liable to occur in weighing out the arsenite of soda or in 

 measuring the amount of other proprietary dips that may be used ; 

 the difficulty encountered in measuring the exact volume of water 

 added to the tank ; the constant evaporation of water that takes 

 place from the tank, and, on the other hand, the occasional flooding 

 By storm water ; the chemical change that takes place in the com- 

 position of the arsenical compounds in the tank. 



Mally (C. W.). Notes on the Use of Poisoned Bait for Controlling the 



House-Fly, Musca domestica, L. — S. African Jl. of Science, Cape 



Town, xi, no. 9, June 1915, pp. 321-32S. [Received 21st Octoler 



1915.] 



The importance of anything which can be used as manure in South 



Africa is such, that its destruction as a means of preventing flies from 



breeding in it is out of the question. Manure repositories have been 



tried and, as is now well known, the heat of the fermenting mass drives 



the maggots to a surface layer 1| to 3 inches deep, in which they can 



be handled by chemical methods. If however the work of piling and 



levelling the manure is done in a slovenly manner, the method fails in 



consequence of the migration of the maggots to cooler portions of the 



heap. The alternative to careful work is to regard the repository 



as a huge fly-trap, screen all openings and kill the flies as they emerge 



