MEAXS OF PREVENTION AND CONTROL 1057 



tive in application. It is obtained by the reaction of milk of lime on a 

 solution of sodium arsenate, viz : 



416 gm [2X03 As04] + 222 g [3Ca (OH)2] = 398 g [Ca^ { AsOi)^] -f 24og [6NaOH]. 



The result is 398 grams of arsenate of calcium and 240 grams of soda 

 or 638 gr. of substances containing in all 150 gr. of arsenic, or 23.5 %. 



The presence of the soda, which remains adhering to the leaves after 

 evaporation, therefore reduces the toxic value of the compound 38 % 



m 



For the rest, a large proportion of the soda ma}'- be allowed to settle 

 at the time of preparation, and if care is taken to use an sodium arsenate 

 absolutely free from chlorides, the calcium arsenate will be superior to 

 all other preparations of arsenic. The most suitable proportions are : 500 

 gr. of sodium arsenate and 200 gr. of fat lime or 380 gr. of calcium hydrate. 



In arsenate of lead the toxic property of the arsenic is added to that 

 of the lead, so that its insecticidal action is in no wa}^ inferior to that of arsen- 

 ate of calcium, but it is much dearer and much more difficult to prepare. 

 It is obtained b}^ allowing a solution of lead acetate to react on sodium 

 arsenate. The percentage of arsenic in the product is 10 %. 



The copper arsenite is obtained by allowing trisodium arsenite to 

 react on a solution of copper sulphate ; the content of arsenic in the 

 product is 17.4 %. 



Finally, iron arsenate and copper arsenate are obtained by causing 

 sodium arsenate to act on a solution of iron sulphate or sulphate of copper; 

 the percentage of arsenic in the product is 17.2 and 16.9 respectively. In 

 spite of the impurities which form in the preparation of the mixtures, cal- 

 cium arsenate is therefore much more active in proiDortion than all the 

 other preparations of arsenic. 



The presence of chlorides weakens the properties of the insecticides. 

 These chlorides may very well be contained no'' only in the arsenate of so- 

 dium, but also in considerable quantities in water, especially in well water 

 (2.5 to 3 gr. per litre). It is therefore preferable to use running water as far 

 as possible. 



To the arsenical preparation Bordeaux mixture is often added, reduc- 

 ing its toxic action. In a i % mixture the weight of the precipitated 

 hydrate of copper oxide is 385 grams per hectolitre; on the other hand, the 

 arsenical mixture obtained with milk of lime and separated from the sodium 

 water contains 398 gr. of arsenical precipitate with a content of arsenic of 

 37.9 % (150 gr.). By mixing the two precipitates, a total weight is obtained 

 of 783 gr. with only 19 per cent of arsenic. 



829 - The Efficacy of Hot Water Treatment against *' Cochylis and " Eudemis,,. — topi 



Mario in Rendiconti dellc sedutc dclla Reale A ccademia dei Lined, Classe di Scienze fisiche, 

 matematiche e natiirali, 5th Series, Vol. XXV, iPt Half Year, Part 7, pp. 524-528. Rome, 

 April 2, 1916. 



M. Semichon, who proposed this treatment, declared it effective against 

 the eggs and larvae of Conchylis ambiguella, Polychrosis boirana and Sparga- 



