MATTH~WS 07t Purifying Coat Gas.

it,troduction of the agates, titus leaving the neck of rite f luk to~gqtt~at as a very convenient handle to lift and carry it by.

He p~rforates the flask by heating a part ~f it ~,ith a !~ot i r ~ f l a d wetting it until a flaw is made, which, by means of-the h ~ x l ~ t ~ he leads around in a proper direction to form the hole. : .

tits furnace consist[d of a small garden pot, about five inclms deeih and four wide, and placed upon a larger pot, inverted ; the hole fii the bottom of the smaller pot being placed over that in the eent~ tff the bottom of the larger one. tie had alsa~ perforated rite aide of tl~ small pot in several places, with holes of three quarters of an inch in diameter, by hotdin~ it against a drill, fixed and turned ia his latho, This pot he partty~illed with charcoal, anti then laying u ~ a tile charcoal a few fine wood shavings, and kindling them, he lax'd mor¢ charcoal upon the kindled shavings, and, by t]~e help of bellowss quickly ignited the whole mass of charcoal. A thin metal plate~ having a circular hole of three inches in diameter in its centre, and laid upon the top of the garden pot, thus converted into a furna¢~ supported lhe Florence ttask and its contents, in a very convenient x l l a I l n e r .

W e like to record these cheap, very simple, slid useful expedients, as they may serve to show how easily a chemical apparatus, necessary in a great variety of operations, may be fi)rmed, even of the com- monest vessels, in the hands of a scientitic individual ; the whole cost of the apparatus would not, probably, exceed sixpence!

~ Tech. Rep,

On Purifying Co~d Gas. By Mr. WII.LI,~.t Ma'vrnEws.

S~R--The art of gas lighting having now become, in a great de~ee, a national coneer~, every eflbrt to improve it may be considered as an endeavour to benefit the public. But circumstances may per- haps have given me apredilection in its favour, as I happened t/~be one of those who had the pleasure of witnessing Mb.17Mtirrlocit,s splendid display at the Soho, near Birmingham, in 180~, and lifter- wards some of Mr. Winsor's exhibitions in London. As I then an- ticipated that its application would eventually be extensive, so I have attentively noticed its progressive advances, and have hailed, with no ordinary interest, every attempt, however trivial, that in the least degree conduced to its improvement.

At an early period of its use, the puritication of coal gas was one of the chief difficulties that attended itsprocesses; but these have long been obviated by the exertions of a few eminent and scientific men. I have seen an account of a process recently introduced atthe Birmingham and Staffordshire gas works, on the principle of a p~t~nt lately obtained there~ I sincerely hope that this improvem~iwill prove to be new. But I presume you arc aware that the ~urification of coal gas, by ammoniacal gas, has long been practised; tara patent for purifying coal gas upon this plan was taken out in 18i7, by Mr. Daniel Wilson, of Dublin; and his specificatior~, with a representation

334 Essays on Lithograph;y~Retouching Ink. of his apparatus, will be found in vol. xxxii, p. 11, of the Repertory of Arts. Perhaos the new method of purifying is an improvement on Mr. Wilson's. "It is stated in a late periodical work, that " M r . B. Cook~ of Birmingham, recommended the use of lime in 1810;" but 1 ]Lave no recollection of ever reading, or hearing, of such a circum- stance before ; and if it be a fact, it has escaped my observation. I have reason to believe that Mr. Murdoch purilied coal gas with lime, in vm'ious ways, twenty-five years ago; and Dr. lIenry notices the washing it width lime-water, in his paper, published in Nicholson's Journal for 18o5. Where, however, ten tons of lime per (lay are used, I am rather curious to learn; the Chartered Gas Works are on a larger scale thanany other in the world; and, no establishment being conducted with greater ability)the skilful superintendents of that very exte)tsive concern must, I presume, have read, with not a little surprise,. . this account of the ¢luantit.y of lime, as well as some other things m that paper. But I am &sposed to suspect that the patentee has been deceived by his inibrmants; tbr, being acquainted with his cha.racter, l am confident he i~ too candid and honourable a man to publish, knowingly and intentionally, any exaggerated or erroneous statemeuts. To excite attention to an iml)ortant object, to correct mis~ tkes,, a l(l, it" l)ossibIe, t ) obtain acc,,,'ate informatio 1, are my only motives lbr writing the al)ove remarks, and your inser- tion of them in your Technological Repository will oblige, sir,

Yours respectfully, 7b T. (in.I., Esq. W. _~lA'r'rrlEws.

Elf~,

ESSAYS ON LITHOGRAPHY.- -No . lV.

Retouching Ink. • " o . 1 V 1 IT sometimes happens, particularly in designs n ado ~ itl the pen~

that the il~k with which they are drawn, has penetrated the stone but slightly. In this case, as tile printing ink~ which is applied by the ,'oiler, does not adhe,'e sufficiently to the slight drawing made upon the stone, a~ ink is used, called by the Germans, 2/nneme fg~rbe, and which unites with, and penetrates more deeply into, the traces made so superficially on the stone. This ink is composed of equal ])arts of linseed oil, suet, and soap, half the quantity of wax, and a little lamp black; the whole is melted and mixed x~ell to~e- ther, and oil of turpentine added to it, when it is desired to makeit more liquid. After having prel)ared the stone, and covered it with gum water, a little of this ink is taken, and, by means of a cleau .tiuml cloth~., rubbed li,htl~ y over every part of the writin¢~,, or draw- ,ng. taking care that it does not eow?r those places on the stone wl{ich are inteuded to remain white. The gum water does not l)t'e- veiit the ink adhering to the lines of the drawing~ but it does no[ al. low it to stick to those parts which are not covered by the litho. graphic ink will~ which tlle designs are made. II, notwithstanding