ART. XXXIX.-On Fumigation. By M. FARADAY, F. R. S., Corr. Mem. Acad. Sciences, Paris, Chem. Assist. Royal Institution, &c. (Jour. Roy. Inst.,

I was called on some months since to direct and superintend the fumigation of the general Penitentiary at Milbank; in doing which some precautions and arrangements suggested themselves, which I have thought might be usefully made known for the information of those who may have occasion to apply disinfecting agents to the purification of buildings, either large or small.

On examining a building to he fumigated, it is necessary to estimate the surface exposed to the infectious vapours, as well as the capacity of the structure. When the air of a

place is impregnated with infectious matter, the surface of the walls &c. will absorb more or less of it in proportion as it is more or less extensive, as it approaches nearer to or is farther from the source of infection, and also in some degree according to its nature.

The general arrangement of the Penitentiary was favourable to its complete and perfect fumigation; for though of great magnitude, yet its division into smaller parts, as galleries, towers, staircases, &c., most of which were glazed, and all of which could be closed by doors so as to separate them from each other, rendered the successive application of the means employed easy and convenient.

After deciding upon fumigation by chlorine, the next object was to ascertain the most favourable mode of applying it; and I was desirous for many reasons of obtaining a gradual and successive developement of the disinfecting agent, rather than a sudden and short one. The latter mode, though it would have filled the building at once, and probably very effectually, yet would seriously have incommoded the operators, and would also soon have disappeared in consequence of absorption by the limed walls, and from dissipation through apertures that would inevitably remain unclosed in different parts of the buildings whilst the former mode by continually supplying the disinfecting agent to the atmosphere of the place for a length of time, would enable it better to act on the bedding, clothing, and other articles left in the cells, and allow it also more perfectly to penetrate to every part of the building itself,

The materials used were those generally employed, namely, common salt, oxide of manganese in powder, and oil of vitriol. Upon making experiments with these substances as furnished by the dealer, for the fumigation, I found that a mixture of one part by weight of common salt and one part of the oxide of manganese, when acted upon by two parts of oil of vitriol previously mixed with one part (by weight) of water, and left till cold, produced the best results. Such a mixture made at temperatures of 60° Fahr. liberated no muriatic acid; but in a few minutes began to evolve chlorine, and continued to do so for four days. When examined on the fifth day, and urged by heat, so as to cause the liberation of all the chlorine that could be afforded by it, only a small proportion was obtained. Such a mixture may therefore be considered as having liberated its chlorine gradually but perfectly, without the application of any extraneous heat; and is therefore very proper for extensive fumigation.

The vessels in which the mixture is to be made should be flat, and such as, being economical, are least acted on by the chlorine or acid. Common red pans were used in the Penitentiary; for many being required at once, better earthenware would have been too expensive. They held each about four quarts.

Preparatory to the fumigation, a quantity of the salt was turned out, the lumps broken down by a mallet until the whole was in powder, and then an equal weight of the oxide of manganese added, and the whole well mixed. The acid and water were mixed in a wooden tub, the water being put in first, then about half the acid was added, stirring at the same time. When the heat produced has been dissipated, which happened in a few hours, the rest of the acid was added, stirring as before, and the whole left till cold. The men used measures in mixing the acid and water, and were told to take rather less of water than of acid, nine measures to ten being nearly the quantities required. Any slight departure from these proportions would be of no consequence. The pans were then charged, each with about 34lb. of the mixed salt and manganese, and distributed at proper intervals along the galleries, &c., care having been taken previously to close the doors and windows, and to stop with mats or rugs all apertures to which access could be had, especially key-holes, through which there was any draft. The diluted acid being cold was then carried in cans or jugs, and measured out in the proportion of 44lb. to each pan, the mixture being well

stirred with a stick, and left to itself. This was done without any inconvenience to the operator, except when the acid was applied too warm: there was abundant time to go from pan to pan, and to close the various galleries in succession. On entering a gallery a few minutes after it had been thus treated, the general diffusion of the chlorine in the atmosphere was sufficiently evident. In half an hour it was often almost impossible to enter, and frequently on looking along the gal lery (150 feet in length,) the yellow tint of the atmosphere could easily be perceived. Up to the fifth day the odour of the chlorine could generally be observed in the building. After the sixth the pans were removed, though sometimes with difficulty, to be emptied and used elsewhere; and the place fumigated, had its windows and doors thrown open.

It was estimated that the charge of each pan would yield about 1lb. of chlorine, or 5 cubical feet. The whole quantity of materials used was 700lb. of common salt, 700lb. oxide of manganese, and 1400lb. of oil of vitriol. The space requiring fumigation amounted to nearly 2,000,000 cubical feet, and the surface of the walls, floors, ceilings, &c., exclusive of furniture, bedding, &c., was about 1,200,000, square feet. This surface was principally stone and brick, most of which had been lime-washed. The space was divided into 72 galleries of 150 feet each in length, and towers, passages, chapel, &c., equivalent to about 13 galleries more. The number of cells, rooms, &c., was nearly 1200.

It was desirable for many reasons that the Penitentiary should be fumigated in the most unexceptionable manner, and the means employed were therefore applied to an extent probably far beyond that requisite to the destruction of any miasma that might be within it. The proportion of chlorine evolved to the size and surface of the building may be considered therefore as sufficient for a case of the most excessive kind; and though the limits are guessed at rather than judged of by any well-founded rule, yet I should consider from one half to one fourth of the chlorine as quite sufficient for any of the usual cases where fumigation is required.

ART. XL. On the Boiling Points of Saturated Solutions. By T. GRIFFITHS. [Jour. Roy. Inst.]

To examine and determine the boiling points of saturated solutions, and the quantity of salt dissolved at their respective

temperatures, with the view, if possible, of furnishing a useful and interesting table, has been the object of the present series of experiments.

Of the great number of saline bodies, the most important only have been selected; and of them perhaps comparatively few, many others being so exceedingly soluble, and changing their composition by the application of heat, that they have necessarily been excluded from these experiments. The method adopted in ascertaining the temperature consisted in exposing water with great excess of salt, in barrel-shaped porcelain vessels to the heat of an argand lamp, a thermometer being exactly placed in the centre of the liquid. When the solution was in full ebullition, the degree indicated by the thermometer was carefully taken, the barometer on the days the experiments were made, being at 30 inches. In the following Table the first column contains the name of the salt, the second shows the quantity of dry salt in 100 parts of boiling solution, and in the third is given its boiling point.

The quantities expressed in the second column were ascertained by weighing out a portion of the boiling solution, and after expelling its water by heat, taking the weight of the dry salt that remained. In this manner it was expected that very soluble salts would yield the greatest quantity of dry salt, and the highest boiling points. But in many instances this is not the case, and remarkably so with sulphate of soda, its solution containing only 31.5 per cent., and elevating the boiling point of water but one degree.*

The elevation of temperature does not seem to depend upon the quantity of salt present, or its solubility. Tartarate of Potassa, a salt very deliquescent, 68 parts of which are contained in 100 parts of the solution, boils at 234°, whilst Mur. Ammonia, a salt unchanged by exposure to air, of which but 50 per cent. is contained in its solution, boils at 236°. A solu tion containing ninety per cent. of Rochelle salt boils at 240°, whilst one of Acetate of Soda, containing only 60 per cent. of the salt, boils at 256°. Solutions of Prussiate of Mercury and Bi-Tartarate of Potassa boil precisely at the same temperatures, the former containing 35 per cent. of dry salt, the latter only 9.5.

The boiling points of the following solutions have not been accurately determined, on account of the great difficulty of making saturated solutions, but the numbers are probably very nearly correct.

In experimenting with this substance the crystals of the salt were liquefied by heat, and boiled in their water of crystallization.