The large proportions of potash and phosphates contained in the insoluble residues render them well suited for use in the manufacture of artificial manures. As already mentioned, when regarded from a scientific or economical point of view, the yellow prussiate industry is carried on under very imperfect conditions. In addition to the amount of potash, there is a very considerable waste of nitrogen, firstly, because the larger proportion of that element present in the animal substances is not converted into cyanogen at all, but passes off chiefly in the form of ammonia salts; and, secondly, because part of the potassium cyanide which is actually produced is lost by decomposition, and another portion is left in the mother liquor. It has been calculated that out of every 100 parts of ferrocyanide which should theoretically be obtained, 4 parts are lost when fairly pure materials have been employed, and 14 in the case of impure ingredients. The following analyses indicate the percentage composition of two samples of insoluble residue:-- No. 1. No. 2. Sulphate of potash, &c. 9·06 3·21 Phosphates of lime, magnesia and iron 13·74 6·24 Oxide of iron 13·34 19·58 Lime and magnesia 5·08 7·23 Sand and silica 23·97 29·24 Charcoal and moisture 34·81 34·50 ------ ------ 100·00 100·00 According to Karmrodt, the following proportions of the nitrogen contained in various animal substances are actually converted into cyanogen during the manufacture of yellow prussiate of potash:-- Per cent. Woollen rags 16 Horn 20 Leather cuttings 33 Cow hair 14 Dried blood 16 Horn charcoal 56 Rag charcoal 33