BOILED BONES .-,% A MANURE. 197 



in an agricultural district in which animal remains most abound. I 

 shall have occasion to illustrate this point more fully, when in a subse- ' 

 quent lecture I come to explain the natural origin of soils, and to trace 

 their chemical constituents to the several rocky masses from which they 

 appear to have been derived. 



Before dismissing this topic, however, there are one or two proper- 

 ties of this bone earth which are of practical importance, and to which, 

 therefore, I must shortly request your attention. It is insoluble in water 

 or in solutions of soda or potash, but it dissolves readily in acids, such as 

 the nitric or muriatic, and also, though less easily and abundantly, in 

 common vinegar. It exists in milk, arid is supposed to be held in solu- 

 tion by a peculiar acid found in this liquid, and which is distinguished by 

 the name oHaclic acid (acid of milk). 



It is slightly soluble also in a solution of cfirbonic acid, and of certain 

 other organic acids which exist in the soil, and it is by means of these 

 acids that it is supposed to be rendered capable of entering into the roots 

 of plants. Wherever vegetable matter exists, and is undergoing decay 

 in the soil, the water makes its way to the roots more or less laden with 

 carbonic .acid, and thus is enabled to bear along with it not only common 

 carbonate of lime, as has been shown in a previous-lecture (p. 47), but 

 also such a portion of phosphate as may aid in supplying this necessary 

 food to the growing plant.* 



In the bones of animals the phosphate is associated with animal gela- 

 tine, which can be partially extracted by boiling bones in water under 

 a high pressure. It has been observed, however, that the phosphate, 

 when in a minute state of division, is slightly soluble in a solution of 

 gelatine, and hence bones, from which the jelly has been partially ex- 

 tracted by boiling, will be deprived of a certain proportion of their earthy 

 matter also. They will have lost their gelatine, however, in a greater 

 proportion, and hence, if again thoroughly dried, they will contain a 

 larger per-centage of bone earth than when in their natural state. In 

 this country, bones are seldom boiled, I believe, either for the jelly they 

 give, or as in France and Germany for the manufacture of glue, though 

 in certain localities they are so treated in open vessels for the sake of the 

 oil they are capable of yielding. Such boiled bones are said to act more 

 quickly when applied to the land, but to be less permanent in their ef- 

 fects. This may be chiefly owing to their not being so perfectly dry as 

 the unboiled bones. Being thus moist, they will contain, in the same 

 weight, a comparatively smaller quantity both of the animal gelatine 



* If to a solution of bone earth in mnriafic acid (spirit of salt), liquid ammonia (hartshorn) 

 be added, the solution will become mlllty, and a white powder will fall, which is the earth 

 of bones in an extremely minute slate of division. Ifthisjmwder be washed by repeated aifu- 

 eions of pure water, and be afterwards well shaken witli water which is saturated with car- 

 bonic acid, or through which a current of this gas is made to pass, a sensible portion of the 

 phosphate will be found to be talcen up by the water. This will appear on decanting the 

 solution and evaporating it to dryness, when a quantity of the white powder will remain be- 

 hind. Ttie mean of 10 experiments made in this way gave me 30 grains for the quantity of 

 phosphate taken up by an imperial gallon of water. What takes place in this way in our 

 hands, happens also in the soil. Not only does that which enters tlie root bear with it a por- 

 tion of this compound where it exists in the soil, but the superabundant water also which 

 runs off the surface or sinks througli to the drains, carries with it to the rivers in its coursft 

 a still larger quantity of this soluble compound, and thus gradually lessens tliat supply ot 

 pliosphate which either exists naturally iu the soil, or has been added as a manure by the 

 practical agriculturist. 



