278 EAETHY PHOSPHATES. 



supply the carbonic acid required for its solution in rain 

 water. An excellent way is to mix tlie powder vnth 

 farm-yard manure and let the mixture ferment. Among 

 the phosphates of commerce, the guano coming from the 

 Baker and Jarvis Islands are distinguished, before others, 

 by their acid reaction and greater solubility. They con- 

 tain only a small quantity of an azotised substance, no uric 

 acid, and small proportions of nitric acid, potash, mag- 

 nesia, and ammonia. The Baker guano contains as much 

 as 80 per cent., the Jarvis guano 33 or 34 per cent, of 

 phosphate of lime ; the latter having, besides, 44 per 

 cent, of gypsum. In diffusibility, these guanos, when 

 equally finely powdered, approach nearest to bone-dust : 

 their condition also enables the farmer who wishes 

 to accelerate their action, to convert them most readily 

 into superphosphates (100 parts by weight of Baker 

 guano requke 20 to 25 per cent, of concentrated, or 30 

 to 40 per cent, of the lead chamber sulphuric acid). 



The influence of these neutral phosphates upon the pro- 

 duce of a field is generally less marked in the first than 

 in the following years, as it takes a certain time to effect 

 their diffusion through the soil. The speedier or slower 

 manifestation of their action upon a field depends, in a 

 great measure, upon the state of fineness of the powder 

 to which they have been reduced, the gi^eater or less 

 porosity of the soil, the presence in it of decaying mat- 

 ters, and careful tillage ; but, under any circumstances, 

 they require a certain store of soluble sihcic acid, and of 

 soda and potash in the soil. 



The subjoined table givmg the produce obtained, in the 

 years 1847-50, by H. Zenker, at Kleinwolmsdorf, in 

 Saxony, shows the difference between guano and bone- 

 dust as regards rapidity and duration of action. In the 

 first year the guano gave the larger produce, which 



