unvarying intensity, have brought it into great favour with the work.people. And its being free from the inconvenience and danger resulting from the sparks and frequ nt snuffing of candles, is a circumstance of material importance, as tending to diminish the hazard of fire, to which cotton mills are known to be much exposed.

The above particulars, it is conceived, contain such information as may tend to illustrate the general advantages attending the use of the gass light; but nevertheless the Royal Society may perhaps not deem it uninteresting to be apprized of the circumstances which originally gave rise in my mind to its application, as an economical substitute for oils and tallow.

It is now nearly sixteen years since, in a course of experiments I was making at Redruth, in Cornwall, upon the quantities and qualities of the gasses produced by distillation, from different mineral and vegetable substances, I was induced, by some obser. vations I had previously made upon the burning of coal, to try the combustible property of the gasses produced from it, as well as from peat, wood, and other inflammable substances. And being struck with the great quantities of gass which they afforded, as well as with the brilliancy of the light, and the facility of its production, I instituted several experiments, with a view of ascertaining the cost at which it might be obtained, compared with that of equal quantities of light yielded by oils aud tallow.

My apparatus consisted of an iron retort, with tinned copper and iron tubes, through which the gass was conducted to a consider. able distance; and there, as well as at intermediate points, was burned through apertures of varied forms and dimensions. The experiments were made upon coal of different qualities, which I procured from distant parts of the kingdom, for the purpose of ascertaining which would give the most economical results. The gass was also washed with water, and other means were employed to purify it.

In the year 1798 I removed from Cornwall to Messrs. Boulton, Watt, and Co's. works for the manufactory of steam engines, at the Soho foundry, and there I constructed an apparatus, upon a larger scale, which, during many successive nights, was applied to the lighting of their principal building; and various new methods were practised, of washing and purifying the gass.

These experiments were continued, with some interruptions,

until the Peace of 1802, when a public display of this light was made by me, in the illumination of Mr. Boulton's manufactory, at Soho, upon that occasion.

Since that period I have, under the sanction of Messrs. Boulton, Watt, and Co., extended the apparatus at Soho foundry, so as to give light to all the principal shops, where it is in regular use, to the exclusion of other artificial light; but I have preferred giving the results from Messrs. Philips' and Lee's apparatus, both on account of its greater extent, and the greater uniformity of the lights, which rendered the comparison with candles less difficult.

At the same time I commenced my experiments, I was certainly unacquainted with the circumstance of the gass from coal having been observed by others to be capable of combustion; but I am since informed, that the current of gass escaping from Lord Dun. donald's tar ovens had been frequently fired; and I find that Dr. Clayton, in a paper in volume xli., of the Transactions of the Royal Society, so long ago as the year 1739, gave an account of some observations and experiments made by him, which clearly manifest his knowledge of the inflammable property of the gass, which he denominates "the spirit of coals;" but the idea of applying it as an economical substitute for oils and tallow, does not appear to have occurred to this gentleman; and I believe I may, without presuming too much, claim both the first idea of applying, and the first actual application of this gass to economical. purposes. [Phil. Trans. 1808.

CHAP. VI.

PHOSPHORUS OF KUNCKEL *.

Phosphoric Bottles and Matches.

PHOSPHORUS is well known to be a peculiar substance capable of inflaming or emitting a luminous aura, when exposed to the air of the atmosphere in a common temperature, and hence the basis of those curious sticks, matches, and bottles, which have of late

* For other kinds of phosphorus, see the ensuing ch. vii,

years been devised for giving light instantly and spontaneously, as soon as they are uncovered and come in contact with the air.

This has hitherto been regarded as a simple combustible, and must be so regarded at present; though various experiments with very high degrees of voltaic electricity appear to have detected that it is a compound, possessing hydrogen and oxygen with a peculiar base. In consistence it resembles wax; when pure it is nearly of the transparency of gum opal, of a colour varying from amber red to the faintest straw, highly combustible, and when oxygenated producing a strong and peculiar acid.

It was discovered by a German chemist of the name of Brandt, about a hundred and fifty years ago, and the preparation was long kept a lucrative secret in the hands of a few persons. It was how. ever well known, from various facts that had escaped, that it was procured in some way or other from human urine; and it has at length been found that it is in consequence of this substance con. taining a peculiar salt, hence denominated phosphoric salt (a mixture of phosphorus and oxygen), that phosphorus can be procured from it; as it has also that it can in like manner be procured from any other animal substance impregnated with the same material ; and consequently from the bones and crustaceous integuments of animals, in which it exists in a larger abundance, and which are now therefore usually employed for this purpose.

One of the earliest chemists, next to Brandt, who devoted his attention in a very considerable degree towards obtaining this com. bustible was Kunckel. This chemist had seen the new product soon after its discovery by Brandt; and strongly desirous of possessing the secret, he associated himself with a friend of Brandt's, whose name was Krafft, through whom he made an offer to purchase the discovery of its inventor. Brandt consented to disclose it; but Krafft, instead of benefiting his colleague by the communica. tion, paid the money, and retained the secret to himself.

Kunckel at this time knew nothing more of the preparation than that it was obtained by a series of processes from urine, through the medium of fire and with this brief and unsatisfactory outline he set to work, and was at length fortunate enough to discover the method for himself; on which account the substance long went under the name of Kunckel's phosphorus. Mr. Boyle is also considered as one of the discoverers of phosphorus. He communicated the secret of the process of preparing it to the Royal Society of

London in 1680. It is asserted, indeed, by Krafft, that he discovered the secret to Mr. Boyle having in the year 1678, carried a small piece of it to London to show it to the royal family; but there is little probability that a man of such integrity as Mr. Boyle would claim the discovery of the process as his own, and communicate it to the Royal Society, if this had not been the case. Mr. Boyle communicated the process to Godfrey Hankwitz, an apo. thecary of London, who for many years supplied Europe with phosphorus, and hence it went under the name of English phosphorus. In the year 1774, the Swedish chemists, Gahn and Scheele, made the important discovery, that phosphorus is contained in bones of animals, and they improved the processes for procuring it.

The most convenient process, for obtaining phosphorus seems to be that recommended by Fourcroy and Vauquelin, which we shall transcribe. Take a quantity of burnt bones, and reduce them to powder. Put 100 parts of this powder into a porcelain or stoneware bason, and dilute it with four times its weight of water. Forty parts of sulphuric acid are then to be added in small portions, taking care to stir the mixture after the addition of every portion. A violent effervescence takes place, and a great quantity of air is disengaged. Let the mixture remain for twenty-four hours, stirring it occasionally, to expose every part of the powder to the action of the acid. The burnt bones consist of the phosphoric acid and lime; but the sulphuric acid has a greater affinity for the lime than the phosphoric acid. The action of the sulphuric acid uniting with the lime, and the separation of the phosphoric acid, occasion the effervescence. The sulphuric acid and the lime combine toge ther, being insoluble, and fall to the bottom. Pour the whole mix. ture on a cloth filter, so that the liquid part, which is to be received in a porcelain vessel, may pass through. A white powder, which is the insoluble sulphate of lime, remains on the filter. After this has been repeatedly washed with water, it may be thrown away; but the water is to be added to that part of the liquid which passed through the filter. Take a solution of sugar of lead in water, and pour it gradually into the liquid in the porcelain bason. A white powder falls to the bottom, and the sugar of lead must be added so long as any precipitation takes place. The whole is again to be poured upon a filter, and the white powder which remains is to be well washed and dried. The dried powder is then to be mixed with one-sixth of its weight of charcoal powder. Put this mixture

VOL. VI.

H

into an earthenware retort, and place it in a sand bath, with the beak plunged into a vessel of water. Apply heat, and let it be gradually increased, till the retort becomes red-hot. As the heat increases, air-bubbles rush in abundance through the beak of the retort, some of which are inflamed when they come in contact with the air at the surface of the water. A substance at last drops out similar to melted wax, which congeals under the water. This is phosphorus. To have it quite pure, melt it in warm water, and strain it several times through a piece of shamoy leather under the surface of the water. To mould it into sticks, take a glass funnel with a long tube, which must be stopped with a cork. Fill it with water, and put the phosphorus into it. Immerse the funnel in boiling water, and when the phosphorus is melted, and flows into the tube of the funnel, then plunge it into cold water, and when the phosphorus has become solid, remove the cork, and push the phos. phorus from the mould with a piece of wood. Thus prepared, it must be preserved in close vessels, containing pure water. When phosphorus is perfectly pure, it is semi-transparent, and has the consistence of wax. It is so soft, that it may be cut with a knife. Its specific gravity is from 1.77 to 2.03. It has an acrid and dis. agreeable taste, and a peculiar smell, somewhat resembling garlic.

When a stick of phosphorus is broken, it exhibits some appear. ance of crystallization. The crystals are needle shaped, or long octahedrons; but to obtain them in their most perfect state, the surface of the phosphorus, just when it becomes solid, should be pierced, that the internal liquid phosphorus may flow out, and leave a cavity for their formation. When phosphorus is exposed to the light it becomes of a reddish colour, which appears to be an incipient combustion. It is therefore necessary to preserve it in a dark place. At the temperature of 99° it becomes liquid, and if air be entirely excluded, evaporates at 219°, and boils at 554. At the temperature of 43° or 44°, it gives out a white smoke, and is lumi. nous in the dark. This is a slow combustion of the phosphorus, which becomes more rapid as the temperature is raised. When phosphorus is heated to the temperature of 148° it takes fire, burns with a bright flame, and gives out a great quantity of white smoke. Phosphorus enters into a combination with oxygen, azote, hydrogen, and carbon. Phosphorus is soluble in oils, and when thus dissolved forms what has been called liquid phosphorus, which may be rubbed on the face and hands without injury. It dissolves too