Faraday to Charles Lock Eastlake   22 October 1844¹

Royal Institution | 22 Octr. 1844.

My dear Sir

Let me at last report to you my results in reference to the subject to which you called my attention, as well as that of Mr. Brande & Dr. Reid², namely, the probable effect of hydrogen in its application to lime as proposed by Mr. Dinsdale³, for the purpose of ameliorating its qualities in regard to the colours used in Fresco painting⁴. Since you directed my thoughts to the matter I have made many experiments, the general results of which are as follows⁵. I have taken well burnt lime, both Dorking and white lime, and have carefully slaked it and mixed it with water. I have then passed hydrogen gas through some portions in a continuous stream for several hours, and other portions I have placed in contact with hydrogen gas in measured & close vessels for days together, using agitation and other means to favour any effect that might occur; but I have never been able to trace the slightest action of the lime and hydrogen on each other, either by any disappearance of the hydrogen or by any sensible change of the chemical qualities of the lime.

I have also prepared portions of surface for fresco painting, according to my best ability, after the instructions I received from you; some of them being with the lime in its original state and others with the same lime treated with hydrogen; and I have applied to their surfaces, in the manner of fresco painting, three test colours, namely Vermillion, Cadmium orange, and an Arseniate green. These were applied on the 2nd September and have been observed from time to time. They are all changed more or less, but I cannot perceive any advantage possessed by the hydrogenated lime in its action on them[.]

I also placed hair pencils in like mixtures of these limes and water, for seventeen days together, moving them frequently & equally in the course of that time, but I cannot perceive much difference amongst them and the little difference that does occur does not point to the hydrogenated lime.

Led by the statement that the keeping of the lime in a slaked condition for a couple of years is a great advantage to it, I took some specimens from the stores which have been so laid up at the Houses of Parliament, for the purpose of examining them in this respect. It appears to me that this lime (which is in a state of paste) is in a very soft and smooth condition in comparison with what would probably be the condition of lime recently slaked; a condition, which seems to be due to its thorough disintegration as a mass and its separation particle from particle. On analysing it I found that it contained a little carbonic acid but not much; for in 100 parts of the dry substance there were but 5 1/4 parts of carbonic acid; these 100 parts therefore would contain 88 parts of quick or uncarbonated lime and 12 parts of carbonated lime; which considering the processes of burning, carrying, slaking &c that it had to go through, and the necessary time of exposure to air before it was laid up in store, is a very small proportion. I do not believe that the lime which is more than four inches in, from the exterior, has received any portion of carbonic acid during the two years of its inhumation⁶[.]

The result of these investigations therefore is negative i.e. I have not been able to find evidence confirmatory of Mr. Dinsdales views.

In respect of the effect of keeping lime for a time, I am led to think, without however having formed any strong opinion on the subject, that the benefit is due to the fine texture which it gradually acquires; and, as there is no doubt that if two surfaces were prepared, the one with fine sand and lime in particles comparitively [sic] coarse, and the other with the same kind of sand & lime in particles comparitively far more perfectly divided, that these two would act very differently both as to the access of carbonic acid from the atmosphere & the transition of lime dissolved in the moisture of the mass from the interior towards the surface; so, there is every reason to expect that there would be a difference in the degree of action upon the colours at that surface and also in the time at which that action would come to a close⁷[.]

I regret that the general state of my health combined with my necessary avocations prevent me from going further into this subject[.]

I am My dear Sir | Your Very faithful Obedient Servant | M. Faraday

Charles L. Eastlake Esq RA | &c &c &c

Endorsed: 22d Octr 1844 Profr Faraday Respectg Mr. Dinsdale's proposed application of hydrogen to lime. ackd