George Henry Bachhoffner to Faraday   26 August 1858

Royal Colosseum, | Regents Park & Albany Street | London Augst. 26th 1858.

My dear Sir,

I have much pleasure in sending you the result of my experiments on the relative photometric value and consumption of the lime light, compared with an argand coal gas burner consuming 6 cubic feet per hour, under a pressure of 10/10ths. I have not attempted to calculate the ratio of light or cost, thinking you would prefer, from the data given, to do so for yourself. I may add that every care was taken to ensure correct results and sincerely hope they may in some degree assist you in your investigation.

I am, my dear Sir, | Yours faithfully, | Geo H. Bachhoffner

M. Faraday Esq. D.C.L. F.R.S. &c.

Time of observation 10 minutes. Temp. 61°Fah.

The oxygen gas holder is 3ft. 3in. in diameter and 4ft. 4in. high, having a head pressure of 10in of water. This fell during the 10 minutes consumption 1¼in.

The other gas holder of the same dimensions charged with coal gas but, under a pressure of 13in. of water fell during the 10 minutes exactly 1in.

Bunsens Photometer¹ was employed to ascertain the illuminating power of the two lights, the spot disappeared upon the disc when the latter was at 86in from the lime light and 17in from the gas flame.

I find that 21 lbs of the bin-oxide of manganese yields a sufficient amount of oxygen under the above pressure to raise the gas holder exactly 8in. - the cost of the manganese being 9/6 per cwt. The coal gas 4/6 per 1000 cubic feet. 10 cubic feet of which raised the gas holder exactly 10in.