It must not be supposed from these remarks, that discoveries which will enable a man to make any particular invention, can be produced to order; that is only true to a very limited extent. Men are beggars of nature, and must not expect to be permitted to choose her gifts, or dictate what secrets shall be disclosed. We may however be certain that if we acquire a very much greater supply of new scientific knowledge, we shall then be able to perfect many good inventions, though not always of the kind we wish, or in the way we expect. The great sewage question {70} may perhaps be solved in quite an unexpected way, possibly by the discovery of some substance capable of precipitating ammonia and organic matter from their solutions. Nearly all our manufacturing processes are full of imperfections; thus the loss of gas by a single large provincial gas company, after that substance has left the works, amounts to nearly one hundred and fifty millions of cubic feet per annum, and to a value of about £18,000; and the soil of all our large cities and towns is permeated and rendered foetid by coal gas. And it has been stated by an eminent authority in such matters that we might save 500,000 tons of coal a year by economizing the waste heat of furnaces, by purifying the coal, coking it, etc. In a single chemical manufactory, out of about two thousand tons of hydrochloric acid used per annum, about eight hundred tons have been allowed to flow away as a polluting substance, because it was not possible to utilise it. The loss of material from a single large glass works equals fourteen hundred tons per annum, and a value of £8,000. Similar grave defects might be pointed out in nearly all our large manufactures, by those acquainted with the subject.