CHLORINE COPPER SALTS. 365 



A more rapid and more powerful effect is produced if the 

 bleaching powder be treated with dilute acids, when chlorine 

 is evolved, thus : 



CaCl (OC1) + H 2 S0 4 = CaS0 4 + H 2 + Cl a . 



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 % of chlorine by volume should be' present in the air. 

 This would require the consumption of about 21t). or 3Ib. of 

 bleaching powder per J.OOO cubic feet of air space. Usually, 

 however, about half this quantity is employed. 



Chlorine fumigation has been successfully used for disinfec- 

 tion after swine fever* and plague, f 



Other hypochlorites have been used, and a process known 

 as the " Hermite" process, by which sea- water is electrolysed 

 and the fluid so obtained used for disinfecting sewage, &c., 

 depends for its action upon the production during electrolysis 

 of hypochlorites, probably chiefly of magnesium. { 



Copper Salts. Soluble copper salts are extremely poisonous 

 to plants. In water cultures it was found that the presence of 

 0-0055 part of copper sulphate in 100 parts of water was 

 sufficient to kill young wheat plants ; while 0*0049 of the 

 bromide, 0-0050 of the chloride, or O'OOol of the nitrate pro- 

 duced a similar effect.^ On the other hand, insoluble copper 

 compounds not only appear to be non-poisonous but are often 

 taken up by the plant. Haricot beans grew even better in 

 nutrient solutions to which copper oxide had been added. j| 

 Copper is said to be often present in plants to the extent of 

 0-003 %, even on ordinary soils, while as much as 0*056 % may 

 be present in the dry matter of plants growing on soils con- 

 taining much copper.*- In Australia a plant Polycarpcea 



* Klein. t Crow and Browne, 1804 



J See Roscoe and Lunt, J. S.C.I. 1895. -224. 



Coupin, Coint. Rend. 18S8. 400; J.C.S. 1899 abst. ii. 118. 



il Tschirch, Ann. Agron. ISO"), f>44 ; .J.C.S. 18t>6 abst. ii. 328. 



MacDougal, Exper. Stat. Record IS'.tD, '24 ; J.C.S. 1900, abst. ii. 235. 



