The following is a description of the method at one time followed at Manchester, and which, with some modifications, is still employed. The pails having been emptied over a grating which held back the solid matter, the liquid rontents were evaporated to one-tenth of the original hulk, or even lews, in an apparatus called the "concretor", which conaiatcd of a revolving cylinder, 8 feet long,' and 4 feet 6 inches in diameter, having its ends partially closed by annular rings, and fitted inside with scroll-like plates of thin metal The liquid was admitted into this cylinder, and as it revolved, these scroll-like surfaces became wetted; the evaporation was effected by passing heated gases through the cylinder. As these came into contact with the wetted surfaces of the metal scroll-, rapid surface-evaporation took place, the temperature of the liquid, however, remaining low, - so low that, though it was discharged from the cylinder at nearly the consistency of treacle, it was rarely, if ever, at so high a temperature as 130' F.

The hot gases, used for effecting evaporation in the concretor, resulted from the combustion of refuse-material, usually consisting of a small portion of cinders and a large quantity of ashes, together with animal, vegetable, and mineral refuse, forming a compound containing too little manure to be valuable, but quite enough to be objectionable. This mat. rial, so difficult to be disposed of satisfactorily, and often saturated with water, was shot into a furnace of special construction termed the "Destructor", so arranged that the material had to traverse a considerable distance within it, exposed to the products of combustion on their way to the chimney, and to the heat radiated from the roof and sides, before it reached the fire-grate. It was thus effectually dried before any attempt was made to burn it. The products of combustion from this furnace were passed through the "concretor" cylinder to effect the evaporation required there on their way to the chimney. The gases, resulting from the combustion of the materials above described, usually contained a small quantity of sulphurous acid, which was sufficient to slightly acidify the liquid in the concretor. If they did not contain it naturally, a little sulphur must be added for the purpose of producing the acid.

The low temperature was not sufficient to cause any appreciable loss of nitrogen, or evolution of ammonia, from the slightly-acidified liquid undergoing concentration. The concentrated material was therefore a fairly strong manure. A random sample of it had been reported upon by Messrs. Burghardt. Grimshaw. & Co., Dalton Laboratory, Manchester, as "undoubtedly a very strong manure, owing especially to the high amount of available nitrogen which decomposes in the ground, and may be expressed as 9.88 per cent of ammonia".

Refuse fuel, such as that used in the " destructor ", produced a large amount of clinker, which, when ground up with a little lime, formed a strong mortar. The process of concentration was not a source of nuisance. "Even the most offensive putrid urine speedily lost almost the whole of its disagreeable odour when undergoing concentration, doubtless owing to the action of the sulphurous acid upon it."

The process themselves had a little charcoal put into them to deodorize their contents, and render them innocuous, and charcoal might in like manner be added to the concentrated liquid to prevent it from becoming offensive. This charcoal was also manufactured from refuse material; it was composed of carbonized street-sweepings, market-refuse, etc, and needed special apparatus to carbonize it, since the low value did not permit of costly handling, while it was bulky and difficult to separate. The heating was effected by a small furnace fed with cinders and other refuse fuel, while the carbonizing kiln consisted of a rectangular chamber of considerable height, into the top of which the materia] to be operated upon was thrown, and through which it gradually descended as its bulk diminished and the material below was removed. Finally, when sufficiently carbonized, it was withdrawn through a slide in the bottom of the chamber. The fire in the furnace was kept thick, and the supply of air to it small, so as to prevent the admission of sufficient oxygen for perfect combustion; thus the products of combustion from it could only heat, and not burn, the materials with which they came into contact, and they might therefore safely be brought into direct contact with the materials to be carbonized. These products of combustion entered the kiln, or carbonizing chamber, near the bottom, and were guided around it by iron plates which touched the wall at their top edges, but sloped so that their bottom edges were some distance from it. These ran around the chamber in a spiral form, and kept open a passage, along which the products of combustion could always find a way to the chimney, while, as they were open at the bottom, the gases could come into direct contact with the materials in the kilns. The plates becoming heated also helped to dry and carbonize the materials. Finally, the products of combustion were led away to the chimney through a flue near the top of the chamber.

By the above methods, almost the whole of the material which came into the yard was effectually dealt with, and turned into a product of much less bulk, capable of being applied to some useful purpose either as a manure, a deodorant and disinfectant, or as mortar, while there was no need for costly chemicals or extraneous fuel. At the same time, the whole of the matter was rendered harmless, and incapable of spreading infection or disease, for it was purified by fire.

Another apparatus for the disposal of the contents of pails consists of a steam-jacketed cylinder about 13 feet long and 4 feet in diameter, fixed on a hollow revolving shaft, with hollow agitators into which steam is admitted at 60 lbs. pressure. The contents of the pails, mixed with about 1.25 per cent of sulphuric acid, are placed in the cylinder, and the agitators, filled with steam, slowly revolve. About 2 tons of pail-contents, holding at least 83 per cent of water, are reduced in 3 hours to about 4 cwts. of a lumpy dark-red loam, containing only about 5 per cent of water. This is allowed to cool, and then riddled into a powder, which is sold as manure, in some cases being of a value of 6 or 7 per ton. Its chemical analysis is as follows: -

Insoluble silica, .........

3216 per cent

Lime, .. .. .. .. .. .. ..

1.310

Oxide of iron and alumina, .. .. .. ..

0.607

Sulphuric acid, .. .. .. .. .. ..

1.885

Phosphoric acid, .. .. .. .. .. ..

3102

Sulphate of potash, .. .. .. .. .. -

5.586

Chloride of magnesium, .. .. .. .. ..

1.910

Chloride of sodium, .. .. .. .. .. -

5.120

Sulphate of ammonia, .. .. .. ..

22.191

Organic matter, .. .. .. .. .. ..

55.073

Total, ... -

100000

With regard to the dry-earth or pail systems, there can but be one opinion as to their unsuitability for modern civilization, and we must agree with the following conclusions of the committee appointed by the Local Government Board in 1875 to inquire into the various methods of sewage-disposal: - "That the retention .. of refuse and excreta .. in cesspools .. or other places in the midst of towns, must be utterly condemned, and that none of the (so-called) dry-earth or pail systems or improved privies can be approved other than as palliatives for cesspit middens ".

The committee appointed by the Society of Arts in 1876 to inquire into various subjects connected with the health of towns, came to the following resolutions: -

"(1) That the pail-system, under proper regulations for early and frequent removal, is greatly superior to all privies, cesspools, ashpits, and middens, and possesses manifold advantages in regard to health and cleanliness, whilst its results in economy and facility of utilization often compare favourably with those of water-carried sewage.

" (2) That hitherto no mode of utilizing the excreta has been brought into operation which repays the cost of collection.

"(3) That the almost universal practice of mixing ashes with the pail-pro-duets, though it applies there as a convenient absorbent and possibly to some extent as a deodorant, is injurious to the value of the excreta as a manure.

"(4) That for use within the house no system has been found in practice to take the place of the water-closet"

There can be no doubt, however, that for certain isolated houses some other methods than those of water-carried sewage commend themselves to our notice, and the next chapter will consequently be devoted to this problem.