SUPERPHOSPHATE OF LIME. 



279 



and to the fact that phosphoric acid is so ex- 

 tremely esseutial, particularly in the early 

 etages of the growth of the plant, that it will 

 not prosper without it, wliatover we may 

 otherwise eiiii)l(>y as manure. A neiglibor- 

 ing agriculturist during the last year tried to 

 raise a crop of turnips with a good dressing 

 of salt and soot, which contain no phosphoric 

 acid, though ])lenty of ammonia and other 

 fertilizing ingredients, but the result was a 

 total failure. In a garden experiment, I may 

 here observe, I found .sul[)huric acid and wa- 

 ter succeed as well as bones in raising tur- 

 nips, but the soil no doubt contained phos- 

 phoric acid, as well as alkalies, on which the 

 acid could act favorably. 



Before we authoritatively pronounce on the 

 quantity of acid necessarj- to be mixed with 

 the bones, it will be better to inquire into the 

 nature and properties of the substances we 

 propose mixing together. 



Sulj)liuric acid, or oil of vitriol, as it is 

 more freijucntly tcnned, consists of tin; union 

 of two parts by weight of sulphur with three 

 of oxygen gas, and its strength de])ends on its 

 purity and freedom from water, for which it 

 has a remarkable affinity, so much so that if 

 exposed to the air it w^ll cpiickly absorb wa- 

 ter from the atmosphere. Its relative weak- 

 ness, therefore, is owing to the quantity of 

 water mixed with it. In speaking of sul- 

 phuric acid, I must be understood t(j mean in 

 its concentrated state, possessing a specific 

 gravity of from 18-4.') to 18-.50. And it .should 

 be borne in mind, in purchasing the acid, 

 that 50 lbs. of the al)Ove is at least equal to 

 GO lbs. of the specific gravity of 1-71-1, and 

 therefore if the weaker acid is used, its quan- 

 tity must be increased in projiortion to the 

 diminution of its sti-ength. 



On applying the vitriolized bone to the 

 tongue, we find that it tastes both .soiu- and 

 sweet. The sourness arises probably from 

 the ph:)sphoric acid, and tli* sweetness from 

 the gelatine sugiu", which is fonned by the 

 action of the acid on the gelatine, converting 

 a substance very difficult of decomposition 

 into one readily soluble, and wliich can be 

 easily absorbed by plants. When concen- 

 trated acid is mixed %vith a quarter of its 

 weight ot water, the temperature of the mix- 

 ture is raised to 300^, and boils away at a 

 great rate. The action of this heat on the 

 animal part of the bones renders it of a dark 

 color ; but if a small <piantity of acid only be 

 employt^d, the mixture is white, from the 

 carbonate of lime which then predominates. 

 From an average taken from .several anjJyses 

 of bones of man and various animals, the liil- 

 lowiug appeals to be tolerably near the mean: 



Organic matter, consisting of gelatine, cartilage, 



and fat 34 



Phosphates of lime and magnesia 59 



Carbonate of lime 7 



Total 100 



Or, in rough numbers, the organic matter 

 may be regarded as forming one-third and 

 (567) 



the earthy poilions two-thirds. Of coin'se, if 

 the bones ai"e very fresh, the former will lie 

 in larger proportion than one-third ; thus Mr. 

 Hainiam gives it as 4.5 per cent. The above, 

 however, may be considered as a fair average 

 in the state usually employed by fanners. 



Four bushels of bones, which may be con- 

 sideretl to be a fair allowance for an acre, will 

 weigh, in a fine state of bone-dust, about 180 

 lbs.* This quantity contains 12^ lbs. of car- 

 bonate of lime, consi.sting of carbonic acid .5^ 

 parts, and lime 7 parts, which will require 

 10 lbs. of sulphuric acid to convert it into sul- 

 phate of lime or gj-psum. This is the first 

 result of the mixture, and is the cause of the 

 very unpleasant fiunes which are given off, 

 and which consist in fact principally of car- 

 bonic acid disengaged from the carbonate of 

 lime in consequence of the sujierior affinity 

 which lime htis for sulphuiic acid. This re- 

 sult takes place before the acid acts on the 

 phosphates of the bones, and thus it is that 

 when a small quantity of acid has been sprin- 

 kled over bone-dust, the good efi'ect has been 

 but moderate, the carbonate of lime alone has 

 been acted on, and the phosphate of lime has 

 remained undeconqiosed. 



The quantity of phosphate of lime existing 

 in the 4 bushels of bones is about 106 lbs., 

 contahiing 47 lbs. of lime and .^9 lbs. of 

 phcjsphoric acid. If we consider sujier 

 pjiospiiate of lime to conUiin a double por- 

 tion of acid — a fact, however, not quite de 

 cided — then 33 lbs. of sidphuric acid will be 

 recpured, which by uniting with half the 

 lime, or 23.^ lbs., forms gypsum, and leaves 

 the other moiety of lime united with a double 

 portion of phosphoric acid in the state of a 

 superphosphate. Thus, 43 lbs. of acid will 

 be required to effect these changes, leavhig 

 any additionsd quantity for other purposes.! 



Phosphate of lime is a substance very diffi- 

 cult of solution, and thus in a very diy .sea- 

 son the effects of bones are often very slight 

 and imperfect. Sujierphosphate of lime, on 

 the otlier hand, is exti-emely soluble, so much 

 so that the vitriolized bones can be entirely 

 dissolved or suspended in water, and thus ap- 

 plied. This at once explains the cause of the 

 valuable properties of the preparation. The 

 bones in their iratural state are extremely in- 

 dige.stible : the acid cooks them — converts 

 them into a species of souj) which can readily 

 be eaten and digested by the young turnips. 

 The adamantine fetters with which the vari- 

 ous elements composuig bones are bound so 

 compactly together, are, by means of this 

 new agent burst asunder — the compact is 

 broken, and each constituent element is left 

 to pursue its own course and to exercise its 



* I tind that the average weight of bone-dust, as it 

 comes from the mill, is 168 lbs. per 4 bushels, al- 

 though I have found it reach the weight stated in the 

 text. [Avt. 



t 1 do not mean to say that these are the precise 

 changes which take place, but only an approxima- 

 tion to them. Prubably some portion of phosphoric 

 acid may be left in a free state in the prepared 

 mi.Kiure. 



