Appendix. 521 



USES. 



This wash may be used in winter on bushes and trees attacked by 

 scale, or in late winter on bushes attacked by red spider. 



If used in the spring, half the quantity of potassium sulphide should 

 be used. 



FUMIGATION. 



Two substances are used for the purposes of fumigation to kill insects 

 on nursery stock. These are (1) hydrocyanic acid gas and (2) bisulphide 

 of carbon. 



The first-named has proved itself of great value, and abroad is used 

 out of doors to fumigate fruit trees. 



This is not necessary in this country, nor is it done by any fruit- 

 growers. 



The necessity of fumigating nursery stock before planting is now 

 recognised by our most up-to-date growers. 



In some of the Colonies, such as the Cape, all introduced stock is thus 

 treated. 



HYDROCYANIC ACID GAS. 



The proportions of the chemicals used do not vary, but the quantity 

 used of them per cubic foot of space depends on whether the plants are 

 dormant or in foliage, whether they are deciduous or non-deciduous, and 

 according to the variety of plant treated. 



FORMULA. 



Potassium Cyanide (98 p.c.) . . 1 ox. 



Sulphuric Acid (sp. gr. 184) . . . 1 ox. 

 Water 4 ox. 



EXTENT. 



100 to 200 cubic feet for dormant plants, 1,000 cubic feet for green 

 plants. 



PREPARATION'. 



Prepare an air-tight shed or glass-house of known capacity, then pile 

 up the nursery stock to be fumigated. The sulphuric acid and water are 

 then mixed together slowly by dropping the acid into the water, and this 

 is put in an earthen basin. The cyanide is then allowed to fall into the 

 sulphuric acid and water, and at once the fumes arise. 



Specially constructed cheap apparatus are made for this purpose, so 

 that the cyanide can be placed in the acid and water from outside the 

 house, and thus exclude all risk of inhaling the deadly fumes. One of 



