224 



HARD WICKK S S CIE NCE - G SSI P. 



treated are termed " phospho " or "dissolved" 

 guanos. From analyses made by several well-known 

 chemists some forty years ago, the following average 

 results were obtained : — 



But it appears that all the old guano (and phosphate 

 of lime, too,) beds have become exhausted, as the 

 percentage of ammonia in guanos is now a third, or 

 even less, of what it used to be. The use of guano 

 as a manure requires some care, on account of its 

 richness and powerful action. It is best to plough it 

 well into the soil, and in no case whatever to drill 

 it in with the seed. It tends to promote excessive 

 development of foliage, and hence is applicable to 

 grass, although it is often used as a general manure. 



Phosphate of Lime is, however, more universally 

 used for manure than guanos, owing to the expense 

 of the latter. It is very generally distributed in some 

 form or other over England, Europe, and parts of 

 America. Some time back, nodules, oval in shape 

 and consisting chiefly of tricalcic phosphate, were 

 found at Lyme Regis and Lewes. These were 

 termed "coprolites." (kopros, dung, and lithos, 

 stone) by Buckland, who explained their occurrence 

 as being fossilised fcecal matter, the excrements of 

 extinct animals, the internal spiral structure which 

 they exhibited being due to the form of the intestinal 

 canal through which they had passed. But the name 

 "coprolites" is now applied to all phosphatic 

 nodules, however formed. Pseudo-coprolites abound 

 chiefly in Cambridgeshire and Bedfordshire, the best 

 of the former containing about 58 per cent., and of 

 the latter 51 per cent., of tricalcic phosphate. The 

 phosphates of France occur chiefly near Boulogne 

 and in the Ardennes, good samples of the 

 former containing about 46 and of the latter 76 per 

 cent, of tricalcic phosphate. Boulogne phosphates 

 generally contain a large percentage of sand. Cana- 

 dian phosphates are more or less crystalline and may 

 contain about 76 per cent, of phosphate of lime, but 

 with a little calcium fluoride or fluoride and chloride 

 together, and its formula may be written 3Ca 3 (P0 4 ), 

 -f-Ca (F 2 Clo). Sombrerite is probably produced by 

 the action of water or rain filtering through the 

 guano deposits and converting the carbonate of lime 

 of the coral-rock into phosphate. Other phosphates 

 are obtained from Navassa, Curacao, and South 

 Carolina. But phosphate of lime occurs also in other 

 substances ; thus bone-ash (burnt bones) contains 

 about 70 per cent., animal charcoal 70 to 80, and 

 bone-dust 48 per cent. The latter also contains 

 about 4^ per cent of ammonia. But none of these 



phosphates would be of any use as they are, for 

 tricalcic phosphate is practically insoluble in water, 

 and plants can only absorb salts in solution. The 

 phosphates must therefore be rendered soluble, and 

 to do this Liebig in 1S40 suggested treating them 

 with sulphuric acid. The action that takes place is 

 theoretically as follows : — 



Ca 3 (POJ 2 + 2 H„S0 4 = CaH 4 (P0 4 )., + 2 CaS0 4 . 



(Tricalcic phosphate and sulphuric acid give 

 calcium hydrogen phosphate, usually called super- 

 phosphate of lime, and calcium sulphate, usually 

 called gypsum.) 



The phosphates are ground to a fine powder, 

 about half its weight of acid is added, and the whole 

 mechanically mixed. The syrupy super-phosphate 

 is run off the deposited gypsum and dried. The 

 manure then consists of super-phosphate of lime, 

 gypsum, free sulphuric acid and undecomposed tri- 

 calcic phosphate. But we have seen that manures 

 should also contain nitrogen and potash, more 

 especially the former; different substances are 

 thoroughly mixed with the syrupy super-phosphate 

 before drying, and thus form the different special 

 manures, as, for instance, " potato-manure," " turnip- 

 manure," etc. These substances maybe ammonium- 

 salts, generally the sulphate, dried blood (containing 

 from 10 to 15 per cent, of nitrogen), wool-refuse 

 (with 4 to S per cent, of nitrogen), rape-cake (with 

 4 to 5 per cent, of nitrogen), soot, sodium and 

 potassium, nitrates, etc. Owing to the soluble 

 nature of these manures the rain diffuses them 

 throughout the soil. The acid phosphates attack the 

 carbonate of lime there present, and are re-converted 

 into tricalcic phosphate, which is precipitated in, 

 however, a so-finely-divided condition as to be 

 readily decomposed again by the acid juices of the 

 plant. Super-phosphates are chiefly used for turnips 

 and root-crops. 



Seaweed is used near the seaside, and is nearly 

 as valuable as farmyard manure. 



Soot, used sometimes for corn, contains from 1 to 

 3 per cent, of nitrogen. 



Ammonium Sulphate contains about 20 per cent, 

 of nitrogen, but is usually mixed with super- 

 phosphate. 



Sodium Nitrate contains about 15*6 per cent, of 

 nitrogen, and is used as a top-dressing for wheat in 

 March or April, when it can be at once utilised by 

 the crop, as otherwise it would be washed away. It 

 is brought from Peru, where it occurs as an incrus- 

 tation on the soil of some feet thick. It is often 

 mixed with dry super-phosphate. 



Bones may be used whole or ground, but decompose 

 very slowly. They are now generally converted into 

 super-phosphates. 



Kainite contains about 13 per cent, of potash, and 

 consists chiefly of the sulphates of potassium and 

 magnesium, magnesium chloride and water. Its 



