MATERIALS 21 



it himself. It is sold as a dry powder, or as a paste 

 containing 70 to 80 per cent, of the powder ; the 

 paste is much the more convenient and safe for hand- 

 ling. Paris green nearly always causes some scorch- 

 ing of the leaves, often to a serious extent ; this miy 

 be diminished, though not altogether prevented, by 

 the addition of lime, which neutralises any free 

 arsenious acid which may be present. 



(i) Paris green paste . . v to i oz. 



Lime i oz. 



Water 10 galls. 



Put the paste in a small pail, and stand it on a stool 

 in the centre of a tub ; while stirring the contents of 

 the pail with a flat piece of wood, pour water into it, 

 and let this overflow into the tub ; the water will 

 carry over only the finer particles, leaving all lumps 

 behind in the pail ; these are broken up by further 

 stirring. The lime (see p. 36) may then be added 

 to the mixture. It should be kept well stirred 

 during use. 



2. Arsenite of calcium (^Arscuite of lime : London 

 pur-ple). 



(2a) White arsenic ... 2 ozs. 

 Quicklime ... 4 ozs. 



Water .... 10 galls. 



Slake the lime (p. 36), add the powdered white arsenic 

 to it, and boil the mixture with one quart of the water 

 for half-an-hour ; then add the rest of the water. 



London purple is a waste product from dye works, 

 and contains about 75 per cent, of calcium arsenite. 



