ECONOMY OF NITROGEN. 



173 



but which will ultimately force itself upon the 

 public attention. 



Bone-black, or animal charcoal, is largely used 

 for water-filters, in sugar-refining, in the manu- 

 facture of blacking, and as a pigment, and con- 

 tains about seventy per cent, of phosphate of 

 lime. That portion applied for filtering and for 

 sugar-refining finds its way, in course of time, 

 to the manure-manufacturer, and ultimately to 

 the soil. The amount used for blacking and for 

 pigments is evidently squandered about in traces 

 far too minute to be again collected by any hu- 

 man agency. To protest against so long-estab- 

 lished and general a custom as giving a black 

 surface to coverings for the feet, is of course a 

 hopeless task ; yet, if we consider that any ma- 

 terial colored black radiates heat more strongly 

 than the same material coated with any other 

 color, we must admit the folly both of blacking, 

 as applied to boots and shoes, and of the original 

 blackening of shoe-leather before it leaves the 

 hands of the currier. Our universal practice can 

 only be considered rational if we wish to have 

 our feet as hot as possible in summer, and as 

 cold as possible in winter. 



Bone-ashes consist, of course, chiefly of the 

 phosphate of lime, and are mainly utilized in 

 agriculture. But a small portion is used in mak- 

 ing cupells for the assayer, and in the manufacture 

 of opal glass. The phosphorus that enters into 

 these compositions is doubtless lost — certainly in 

 the latter case — but its quantity is not sufficient- 

 ly large to render it worthy of especial attention. 

 Of far more moment is the bone-ash wasted in 

 refining argentiferous lead, no less than seventeen 

 pounds being consumed for every ton of the met- 

 al operated upon. This is, if we refer to our 

 former standard, a quantity nearly sufficient to 

 build up the skeleton of a man. We are not 

 aware that the bone-ash thus employed in refin- 

 ery-hearths is afterward collected and purified 

 from adherent traces of lead, so as to be fit for 

 agricultural uses. 



Many iron-ores contain phosphorus. Thus in 

 vivianite, phosphoric acid may be present to the 

 extent of thirty per cent. In a few instances this 

 constituent is separated in an available form, but 

 in the majority of cases it remains partly in the 

 iron, to the great dissatisfaction of the manufact- 

 urer, who finds his product much impaired, and 

 partly in the slags. Under both these circum- 

 stances it is generally wasted. 



Phosphoric acid, combined with soda or pot- 

 ash, enters into the composition of certain " dung- 

 substitutes" used by the calico-printer. Here, 



again, it must be regarded as ultimately wasted, 

 since, when its purpose is served, it is washed in- 

 to the sewers along with a variety of substances, 

 many of them hostile to vegetable life, and there- 

 fore ill-fitted for application to the soil. 



But even the phosphoric acid that is supplied 

 to the fields in the forms of superphosphate, of 

 bone-dust, Peruvian guano, farm-yard manure, 

 night-soil, etc., and is there assimilated by the 

 crops, is still afterward in great danger of being 

 turned aside from its normal channel of circula- 

 tion, and thus of being substantially lost. Every 

 one in these days has learned that animals, in their 

 excreta — solid, liquid, and aeriform — give back 

 all the matter which tljey have assimilated, and 

 which has for a time formed part and parcel of 

 their bodies. If the solid and liquid excreta? 

 therefore, of all the animals fed upon the prod- 

 uce of a plot of land, of say ten acres in size, 

 together with all the waste or residual portions 

 of the crops, are returned to that plot, its fertility 

 — i. e., its power of producing grain or vegetables, 

 or of feeding cattle — will remain substantially 

 unimpaired. But if this is neglected, or done 

 only in part, a gradual decline of fertility must 

 take place. We may, indeed, by importing bone- 

 ash, Peruvian guano, and the like, keep up the 

 needful supply of phosphoric acid in a ten-acre 

 plot, or possibly in the whole of England ; but 

 this is, in familiar phrase, simply " robbing Peter 

 to pay Paul." The whole accessible store of 

 phosphoric acid on the face of the globe, and 

 consequently the total quantity of wheat and of 

 beef that can be produced, and the number of 

 human beings that can be maintained, is lessened 

 by every gallon of sewage we pour into a tidal 

 river or into the sea. To put the fact in another 

 light : every stroke of the costly and ornate 

 pumping-engines at Barking Creek and at Cross- 

 ness is destroying potential life, or rendering 

 existence more difficult throughout the world ! 

 Surely this is an outcome of engineering skill on 

 which the nineteenth century has small cause for 

 self-congratulation. 



It is indeed true that the phosphoric acid 

 thus so bountifully poured into the sea may be, 

 in the lapse of years, recovered in the shape of 

 fish, serviceable for food or for manure ; but this is 

 a long, a tedious, and a doubtful circulation. If 

 the excreta of men and animals are placed upon 

 arable soil, their valuable constituents are rapid- 

 ly made available and assimilated by plants, and 

 may reappear within a twelvemonth in the shape 

 of food ; but if poured into the sea their phos- 

 phoric acid, etc., will probably be first absorbed 



