[Should farmers burn bones before using them? How would you compost bones with ashes? In what way would you prevent the escape of ammonia?] _Bone-black._ If bones are burned in retorts, or otherwise protected from the atmosphere, their organic matter will all be driven off, except the carbon, which not being supplied with oxygen cannot escape. In this form bones are called _ivory black_, or _bone-black_. It consists of the inorganic matter, and the carbon of the bones. The nitrogen having been expelled it can make no ammonia, and thus far the original value of bones is reduced by burning; that is, one ton of bones contains more fertilizing matter before, than after burning; but one ton of bone black is more valuable than one ton of raw bones, as the carbon is retained in a good form to act as an absorbent in the soil, while the whole may be crushed or ground much more easily than before being burned. This means of pulverizing bones is adopted by manufacturers, who replace the ammonia in the form of guano, or otherwise; but it is not to be recommended for the use of farmers, who should not lose the ammonia, forming a part of bones, more than that of other manure. _Composting bones with ashes_ is a good means of securing their decomposition. They should be placed in a water-tight vessel (such as a cask); first, three or four inches of bones, then the same quantity of strong unleached wood ashes, continuing these alternate layers until the cask is full, and keeping them _always wet_. If they become too dry they will throw off an offensive odor, accompanied by the escape of ammonia, and consequent loss of value. In about one year, the whole mass of bones (except, perhaps, those at the top) will be softened, so that they may be easily crushed, and they are in a good condition for manuring. The ashes are, in themselves, valuable, and this compost is excellent for many crops, particularly for Indian corn. A little dilute sulphuric acid, occasionally sprinkled on the upper part of the matter in the cask, will prevent the escape of the ammonia. [What is the effect of boiling bones under pressure? How is super-phosphate of lime made? Describe the composition of phosphate of lime, and the chemical changes which take place in altering it to super-phosphate of lime.] _Boiling bones under pressure_, whereby their gelatine is dissolved away, and the inorganic matter left in an available condition, from its softness, is a very good way of rendering them useful; but, as it requires, among other things, a steam boiler, it is hardly probable that it will be largely adopted by farmers of limited means. Any or all of these methods are good, but bones cannot be used with true economy, except by changing their inorganic matter into SUPER-PHOSPHATE OF LIME. _Super-phosphate of lime_ is made by treating phosphate of lime, or the ashes of bones, with _sulphuric acid_.