SODIUM NITRATE (NITRATE OF SODA). 107 



fallow, as the latter is incapable by itself of diminishing the number 

 of polyphagous larvae. 



Pieris (white cabbage butterfly). — The grubs of the Pierides, 

 which ravage cabbages, may be destroyed by watering the latter with 

 a solution containing 250 grammes of salt and 250 grammes of 

 tobacco juice in 14 litres of water, say 1 lb. salt and 1 lb tobacco 

 juice in 5-6 gallons of water. 



Salt has been used to kill plant lice. 



Phylloxera vaslatrix, Planch, (phylloxera). — Salt, recommended 

 by so many practical men to kill the phylloxei'a, has been found by 

 Mouillefert as absolutely inactive. A dose inconvenient to this plant 

 louse would be quite as injurious to the vine, because the latter dies if 

 the soil contains a certain amount of salt. According to the experi- 

 ments of Viola on the vine in pot. a dose of 200 grammes, say 7 oz.. 

 kills this plant in eight days. 



Schizoneura lanigera, Hausm. (woolly aphis). — Krafft recommends 

 the following emulsion, which yields a satisfactory result : Petrol 

 800 cubic centimetres, salt water, 25 per cent, 200 cubic centi- 

 metres. 



Aspidiotus perniciosus, Comst. (the San Jose louse). — In California 

 there is employed against this cochineal a mixture of lime, sulphur, 

 and salt, but this preparation has been abandoned in the Eastern 

 states owing to certain failures, and better results got by the use of 

 whale-oil soap-emulsions. 



Use of Salt to Preserve Green Fodder during Winter. — 1. Plants 

 mowed green are left on the ground for one or two days. They 

 partially dry and lose about half their weight. They are then conveyed 

 into rectangular pits, l"7-2 metres deep, dug out of compact ground, 

 clay, if possible. A layer of the mown plants is laid 15-20 centimetres 

 (6-8 inches) deep, which is compressed under foot then sprinkled with 

 a thin layer of salt. Another layer of plants is laid down, then a layer 

 of salt, and so on, until the pit is completely full, and even to 1 metre 

 (40 inches) or 1-3 metre (53 inches) above the level of the ground. 

 Care must be taken to spread the salt in larger quantities on the edges 

 and corners of the pit. The whole is afterwards covered with a layer 

 of 60-70 centimetres (24-28 inches) of soil. The fissures produced dur- 

 ing natural shrinking should be stopped. The cover is in the fox'm of a 

 sloping roof. This cover is absolutely necessary. For a ton of beet 

 leaves it requires 24-3 kilometres of salt, say 5*5 to 6-6 lb. The 

 ensilage should not last more than two days. Fermentation soon 

 commences, and reduces the mass to half its bulk. The fodder extracted 

 from these silos may be given as food to animals without injuring their 

 health. 



2. Moist hay is dried and mixed with salt. Sinclair, Hell (?Hill), 

 Kauslei% Flandrin, and Schattenmann, recommended to sprinkle the 

 different layers of hay with salt in proportion as they enter the silo. 

 The salt absorbs the moisture and preserves the hay from all fermen- 

 tation and mould. The dose should be 2 kilogrammes (4-4 lb.) per 

 metric ton of hay. 



26. Nitrate of Soda, NaNO„. — Occurrence. — Nitrate of soda or 



