XVII. MISCELLANEOUS PKODUCTS USED IN AGRICULTURE 361 



focation, partly by condensing on the walls of the working and on the 

 stores of food and thus rendering these poisonous to any insects which 

 may escape suffocation. 



Arsenic, generally in the soluble form of sodium arsenite, is the 

 chief ingredient of many sheep-dips. 



In many hot countries, dipping of both cattle and sheep is chiefly 

 directed to the destruction of ticks which play so important a part in 

 the transmission of disease. In South Africa and in Australia, practical 

 experience has led to the conclusion that the dipping solution must 

 contain about 0'2 to O3 per cent of soluble arsenious oxide in order to 

 be effectual. Tar, soap, aloes and other substances are sometimes 

 added to the dipping solution, but apparently have little effect upon the 

 ticks, though they probably serve a useful purpose in rendering the 

 liquid unpalatable and thus less likely to poison the cattle or sheep. 



If animals be dipped in too strong an arsenical solution or if 

 dipped when hot through exercise, poisoning through absorption of 

 arsenic by the skin may ensue. Sheep are more likely to be affected 

 than cattle or horses. 



In South Africa a dip containing 



Arsenite of soda . . . . . . . 5 lb. 



Aloes fib. 



Soft soap . . 5 lb. 



Water 100 gallons. 



is recommended. For long woolled sheep, the soap is better omitted- 

 Arsenite of soda is also used, under the name of " Scrub extermi- 

 nator," as a plant poison, particularly in the destruction of prickly 

 pear. 



Bleaching PowderChloride of Lime, Ca(OCl)Cl, is used 

 chiefly as a disinfectant. It acts by evolving hypochlorous acid, 

 HC10, which is a strong oxidising agent and thus able to destroy pu- 

 trescible matter and micro-organisms. The hypochlorous acid is set 

 free by the carbon dioxide of the air, thus : 



2CaCl(OCl) + CO, + H 2 = 2HC10 + CaCl 2 + CaC0 3 . 



A more rapid and more powerful effect is produced if the bleach- 

 ing powder be treated with dilute acids, when chlorine is evolved, 

 thus : 



CaCl(OCl) + H 2 S0 4 = CaS0 4 + H 2 O + C1. 2 . 



The chlorine acts as a most effective disinfectant. It very rapidly 

 destroys micro-organisms, even when much diluted with air, but is, 

 like all disinfectants, less successful with their spores. According to 

 Fischer and Proskauer, to be effective, about 0'5 per csnt of chlorine 

 by volume should be present in the air. This would require the con- 

 sumption of about 2 lb. or 3 lb. of bleaching powder per 1000 cubic 

 feet of air space. Usually, however, about half this quantity is 

 employed. 



Chlorine fumigation has been successfully used for disinfection 

 :after swine fever and plague. 



