222 THE CULTURE OF FARM CROPS. 



farmers with marked benefit on thin light soils, adding more 

 than one ton of hay per acre to the usual yield of 2J tons. 

 This fact, considering that England is surrounded by tha 

 ocean, and no part of it is beyond the influences of the moist 

 winds which come over the sea, effectually disposes of the 

 objection that salt is of no value upon land subject to the 

 influences of the sea air. No doubt there are many cases 

 in which no good results have been derived from the use of 

 salt. But this may be taken as a proof that the land in 

 such cases has been already fully supplied with it and that 

 some other kind of plant food was needed. 



A very interesting experiment to show whether the soil 

 contains salt in any appreciable quantity may be made as 

 follows : one pound of the soil is taken in dry weather and 

 washed with a pint of distilled, or pure rain water. The 

 water is filtered through unsized or blotting paper and the 

 clear liquid is collected in a clean glass bottle. If salt is 

 present in the water, a white precipitate will be thrown 

 down on the addition to it of a solution of nitrate of silver. 

 Every 10 grains of the dried precipitate represents 4 grains 

 of salt in the pound of soil tested. If a pound of soil yield 

 one grain of salt, it will be equal to 500 Ibs. upon an acre 

 12 inches deep. If no more than this is contained in the 

 -soil, it will be very safe to conclude that salt may be use- 

 fully applied to it. 



GUANO, may properly be classed among mineral man- 

 ures; for although it has been supposed to have been de- 

 rived from the droppings of sea birds upon the islands where 

 it has been procured, yet it is quite certain that some of the 

 guanos imported and used as manure are of mineral origin 

 although perhaps it has been like coal derived from or- 

 ganic matter. The composition of guano varies considera- 

 bly. Formerly the best guano brought from Peru and the 

 adjacent islands, contained as much as 17 or 18 per cent, of 

 ammonia, and from 30 to 45 per cent, of phosphate of lime ; 

 and was sold at the high price of $150 to $200 per ton. The 

 best now imported has only from 7 to 10 per cent, of am- 

 monia and 25 to 30 per cent, of phosphate of lime; while 



