360 AESENIC AS AN INSECTICIDE 



are much less injurious, for plants will grow in solutions containing as 

 much as 0'02 per cent. 1 



Arsenious oxide is sometimes used in medicine as a nerve tonic, 

 and by repeated small doses, a person may acquire the power of taking, 

 without danger, quantities which far exceed the normal lethal dose. 

 In such cases, however, ill effects upon the system are generally pro- 

 duced by continual dosing with arsenic. The administration of arsenic 

 in small quantities often produces a plumpness and sleekness of the 

 skin. For this reason it is often secretly given to horses by farm 

 servants, often with fatal results. Considerable publicity was given to 

 the prevalence of this practice in the north of Yorkshire a few years 

 ago, and many cases of serious losses of horses occurred from this 

 cause. 



Arsenious oxide finds a more legitimate use in sheep dips, especi- 

 ally for foot-rot and as a vermin poison. 



In South Africa enormous quantities of arsenical compounds are 

 used for the destruction of locusts. In its adult stage as a flying 

 insect the locust is difficult to deal with and reliance is chiefly placed 

 upon methods of attacking it while in the immature, hopping stage. 

 These "voet-gangers," as the young locusts are called, travel in vast 

 armies across the country and devour and destroy all vegetable matter 

 which lies in their path. The most successful method of coping with 

 them is to spray the grass or other vegetation in front of the advancing 

 swai-m with a solution containing sugar and arsenite of soda, the 

 strength varying from 1 Ib. of arsenite and 2 Ib. of sugar to 16 gallons 

 of water for the very young insects, to 1 Ib. of arsenite and 1 Ib. of 

 sugar to 8 gallons of water for the almost full-grown voet-ganger. In 

 this way many thousands of swarms have been destroyed. Many 

 tons of arsenite of soda have been used, and, mainly owing to care- 

 lessness, poisoning of cattle, sheep and goats has been somewhat ex- 

 tensive. 



The vegetation sprayed with the solution, if not eaten by the 

 locusts, quickly dies, and if animals are not allowed access to the 

 place until after rain has fallen, little danger of poisoning stock is ex- 

 perienced. 



Whit 3 ants, also very abundant and destructive in South Africa, 

 are often destroyed by means of arsenic. 



A special apparatus is used, in which a mixture of about 9 parts of 

 arsenious oxide with 1 part of sulphur is strongly heated by burning 

 wood or coke, and the vapours forced, by means of a pump and 

 flexible tuba, into the ants' nest, which is often deep below the 

 ground. 



The vapours thus introduced destroy the ants, partly by direct suf- 



more than traces of arsenic in the preparation of these substances. According to 

 Haselhoff (Jahresbericht ii. Agricultur-Chemie, 1900, 126) superphosphate made 

 with sulphuric acid from German pyrites contains about 0-05 per cent of arsenic; 

 with acid from Spanish pyrites, as much as 0-149 per cent of arsenic. He con- 

 cludes that little danger exists of the arsenic in superphosphate being sufficient to 

 do harm. 



^toklasa, Ann. Agron., 1897, 471 ; Jour. Chem. Soc., 1898, Abstracts, ii. 131. 



