The Collodion Process in Photography. ~05

the side of the river, which was, of course, an advanfag% the : 'wiligat being all the time out in the river. The paddles revolved at the rate of 40 per minut% and the boats moved at the same speed until they passed Westminster Bridge; but on passing Vanxhall Bridge, the Twi@'htgot considerably ahead~ and on passing Chelsea Hospital, at 39 minutes past 2 o'clock, she was about 300 yards ahead of the Bridegroom~ and the paddles were then making 44 revolutions per minute, until she arrived at Cadogan-pier. It was stated that the number of revolutions of the paddle wheels on board the Bridegroom averaged 441- per minute, and on board the Twili<¢ht 42 per minute. The vibration in the Twilight was scarcely perceptible in the run both up and down the river> which, together with the steadiness of ~aotion produced by the fan paddles~ the efl~ct was very agreeable.

it is,. understood, that. the fan. t~addle, is. to be nip ) lied to one of the lar_ce, o sea-going steamers, w~th a vtew to increase her speed, and to get nd of the vibration now caused by the ordinary paddles.

~b £ncrease t/ze I22~mi,nati~ Power of Gas.*

In one of your ]ate numbers~ you allude to a recent patent for improve- ments in the manufacture of gas, the object of which is to render the gases resulting fi'om the decomt~osit[on of water suitable for lighting pur- poses, by passing them over cannel coal in the process of distillation. I wi~:nessed some experiments of this nature with the gases obtained from wood in the manufheture of pyrdigneous acid, and have myself~ for some time past, been making ,~ series, using several descriptions of slightly illuminating gas, but principally those given out by peat and the lowest quality of" coals~ and the results are highly interesting. I find that a cer- tain volume of such gas when passed through a heated retort containing Lancashire cannel coal, becomes of much greater illuminating power tt-au the same volume of such gas mechanically mixed in a gasholder with the gas given out by the cannel; indeed, some of my experiments show this increase to be at least 50 per cent. when our common coal gasis so treated, as I0,000 feet of it may be passed through the retorts containing a ton of Lancashire cannel in the process of distillation, and the result will be ~0,000 feet of gas equal in quality to that given out by the cannel alone, and it incurs no perceptible deterioration by being retained in a gasholder for several days. C.C.

The Collodion Process in Photography. By FRED. ScoTT A~eg~.~"

"I am anxious to eommunicam to those engaged in the Coilodlon pro- cess in Photography an Improvement in the mampulatlon Whmh I beheve will be found to facilitate the process considerabl:y. It is, theuse of tile upright glass bath for the nitrate of' silver solution:--andi will endeavor, in as few words as possible, to explain my mode Of using it. The bath is about three parts filled with a solution of nitrate oflsil~er of the usual

* From tile London Builder, No. 461. "i" From the London Athenmum, ~ovember, 1851. ¥o~. XXIII.~T~nt~ S~ai~s.--No. 3 .~M~ac~, 1852. 18