Bone Dust, bones crushed and ground to dust for manure. The finer the dust the more rapid is its action; the coarser the particles, the longer is their effect slowly given out. This substance is beneficial to the growth of plants from its affording them several of the constituents they require. The following analysis of dry ox bones is by Berzelius:

Phosphate of lime, with a little fluoride of calcium.

. 57.35

Bone gelatine .............................................................

. 33.30

Carbonate of lime .......................................................

. 3.85

Phosphate of magnesia ...............................................

. 2.05

Soda, and a little chloride of sodium..............

3.45

100.00

The phosphate of lime of the solid bone, and the ammonia furnished by the organic matters connected with it, are particularly beneficial. So valuable is this substance regarded as a manure in England, that in the report of the Don-caster agricultural association it is stated that one wagon load of small drill bone dust is equal to 40 or 50 loads of fold manure. Upon thin and sandy land it is particularly effective, and continues to act for several successive crops. It is best applied when mixed with earth and fermented, and at the rate of 25 bushels of fine bone dust and 40 of broken bones to the acre. It is also used as a top dressing, sown broadcast and by the drill. Pasture and grass lands are greatly benefited by it; white clover springs up wherever it falls; and the turnip crop is largely increased by its- application. Bone dust is sometimes adulterated with the raspings and filings of the ivory nut. - In this place the use of dissolved bones and other , phosphates, first recommended by Liebig in ' 1840, may be noticed. The phosphatic mate-; rials are first ground to a very fine powder by millstones; the powder is then carried up by means of elevators and discharged continuously into a long iron cylinder, having agitators revolving within it with great velocity.

A constant stream of sulphuric acid, sp. gr. 1.66, enters the cylinder at the same end as the dry powder, and the mixture flows out at the other end in the form of thick mud, having taken three to five minutes in passing through the machine. The quantity turned out by such a mixing machine is about 100 tons daily. The semi-fluid mass runs into covered pits 10 to 12 feet deep, each of sufficient size to hold the produce of the day's work. It becomes tolerably solid in a few hours, but retains a high temperature for weeks, and even months, if left undisturbed. The composition of a superphosphate of good quality, made partly from mineral phosphate and partly from ordinary bone, may be stated as follows:

Soluble phosphate .........................

22 to 25 per cent.

Insoluble phosphate ..................

8 to 10

Water ...............................

. 16 to 12

Sulphate of lime ........................

35 to 45 "

Organic matter .........................

12 to 15 "

Nitrogen ................................

0.75to 1.5 "

If sufficient sulphuric acid were used to decompose the whole of the phosphate of lime, the product would be too wet to be packed in bags, and would require either to be mixed with extraneous substances of a dry and porous nature or to be artificially dried. The manufacture of manures from guano, from the Ashley river deposits of South Carolina (see Oo-peolites), and from the mineral apatite, has become an industry of great importance. The commercial superphosphates are so frequently adulterated that purchasers would do well to have the samples analyzed before contracting for large quantities.