276 The Phosphates used in Agriculture. 



of lime. Sucli are the phosphates known as " West India phos- 

 phate/' " Bolivian guano/' etc. These contain from 40 to 60 

 per cent, (and sometimes more) of ordinary phosphate of lime, 

 whilst their per-centage of nitrogen (ammonia) dwindles down 

 to 2, 1, or even 0'5 per cent., as the phosphate increases. 

 Here, then, is an abundant source of phosphate of lime. 



But several West India islands furnish a species of hard 

 rock, of very peculiar aspect, consisting chiefly of phosphate of 

 lime. Many persons consider that this rock has been derived 

 from guano, supposing it to be the result of exposure to the 

 atmosphere for thousands of years; others imagine it to be 

 guano modified by volcanic action. I have examined this 

 mineral phosphate,* and find that it contains not only phosphate 

 of lime, but also a considerable proportion of phosphate of 

 alumina — a substance not met with in guano : it is, in fact, a 

 compound of phosphate of lime and phosphate of alumina, con- 

 taining about 17 per cent., of the latter, and 65 per cent, of 

 the former. As this rock is principally derived from the little 

 island of Sombrero, I called it Sombrcrite. This is another 

 tolerably abundant source of phosphate of lime, much used in 

 the manufacture of superphosphate manure. 



Another hard phosphatic rock, of a similar description, is 

 found upon Monk Island, in the Gulf of Venezuela. Although 

 I have received for analysis in my laboratory many hundred 

 specimens of the different phosphates mentioned in this paper, 

 I have never yet met with this one from Monk Island j but I 

 have reason to believe it is a substance similar in all respects 

 to Soinbrerite. Whether it be so or not cannot bo determined 

 by the few incomplete analyses that appear to have been made 

 of it hitherto. However, it constitutes a cheap source of phos- 

 phate to manufacturers of superphosphate manure ; and it 

 appears to contain 78 to 80 per cent, of phosphate of lime. 



Another, and most abundant source of phosphate of lime is. 

 I am happy to say, an indigenous one, and one which is very 

 extensively utilized in the manufacture of superphosphate. I 

 allude to bh» Cambridge and Suffolk eoprolite». These are hard 

 nodules, somewhat cylindrical, and haying rounded edges. 

 The Cambridge coproHtes are found in the upper green sand, 

 where they form extensive deposits, and are so intimately 

 mixed, OS their smTaee, with the green Band il self, that then* 

 true colour is only seen when they are broken. They contain 

 60 to 66 pei- cent, of phosphate of lime, sometimes rather more, 

 and when ground form a yellowish-white powder. They are 

 supposed to be fche fossil excrement of extinct animals, hence 

 their curious name, derived from the Greek; but wo have not 



* Journal of the Chemical Society, 1862. 



