James Thomson to Faraday   9 November 1858

2 Donegall Square West, Belfast, | 9th Nov. 1858.

My dear Sir,

I thank you very much for having so kindly written to me in August last on the subject of the freezing and melting point of water & ice¹. I intended to write to you at the time, thanking you for your letter; but, through illness in my family, and repeated absences from home on business, I have hitherto found myself detained from reverting to the subject.

I recollect that in the old Athenaeum report of your Paper² - to which however I have not had access of late - mention is made of your supposition that there is a tendency for a film of water between two surfaces of ice to become ice, other particles touching ice only on one side becoming water at the same time, and supplying the cold necessary to freeze the water between the two surfaces of ice. Having been long aware of that supposition, and now having farther had your letter of August 4 to consider; I still incline to think that the freezing of the film between the two masses of ice is due simply to the melting by pressure of portions of the ice pressed against one another at places of contact.

Soon after the time when I received your letter, I met with a paper by Prof. Forbes of Edinburgh (from the proceedings of the Royal Society of Edinburgh dated the 19th of April 1858) “On Properties of Ice near its melting Point.”³ This I presume to be the paper in which his shilling experiment is mentioned to which you alluded in your letter to me. In that paper Forbes states an experiment as proving that two masses of ice placed extremely close to-gether, and having a film of water intervening, but free from pressure against one another, will unite even in a moderately warm atmosphere. I am not, however, prepared to admit the validity of his proof in this matter. He had slight springs pressing the masses of ice together: but beyond this I conceive that the capillary attraction of the intervening water would draw the masses against one another with a force quite notable:- and also I conceive that the film of water between the two masses of ice would be sustained almost entirely by capillary attraction at its upper surface, and would therefore exist (like mercury in a barometer) under a pressure less than that of the atmosphere. This diminished fluid pressure would raise the freezing point of the film of water, and would produce a tendency to its freezing, even by contact with such parts of the adjacent ice as exist under atmospheric pressure, and much more by contact with the parts of the two masses of ice in contact with one another and pressing against one another by the forces of the spring used to maintain contact and of the capillary attraction of the fluid pulling the masses against one another.

Thus I still incline to think that mere proximity is not enough to cause the two pieces of ice to unite.

In your letter to me you make reference, as bearing on this subject, to what appears to be a very general law, namely that, in bodies of the same kind, the particles tend to retain the state of those which surround them:- as, for instance, that water may be cooled much below 32°F. without freezing; but that a splinter of ice touching it will instantly make it solidify: and that water may be raised under atmospheric pressure to a temperature far above 212°F. without boiling but that a bubble of air introduced will cause it to explode. It seems to me, however, that these phenomena are essentially distinct from what can occur with a film of water touching ice on one side, or on two opposite sides: because, in the phenomena you adduce the tendency is for a particle to retain a state in which it already exists, that state being the same as the state of the surrounding ones: but I do not think they show a tendency for a particle differing in its state from the surrounding particles to assume their state. It is certain that, in numerous cases, every particle shows a great resistance to change from a state in which it and all adjacent particles exist. In the case of a film of water between two masses of ice, however, the difficulty of making a beginning either of melting or freezing does not exist, as both water & ice are present to-gether.

I do not see in the principle I have proposed any insufficiency to explain the regelation of fractured ice, & the plasticity of ice; and, according to the views I have just now submitted, I do not see that we ought to suppose the occurrence of another efficient cause of regelation such as you have suggested.

With great deference I beg to offer the above remarks to you.

I am, With thanks, | Yours most truly, | James Thomson.

P.S. It may be well to mention that I conceive the powerful tendency to adhesion manifested between flannel & ice in a warm atmosphere, is to be attributed partly to the fibres of the flannel being drawn against the ice by capillary attraction of the liquid films, & thus being made to apply a pressure to the ice which must slightly lower its melting point; & again partly to the diminished fluid pressure of the liquid films produced by capillary attraction, which must raise the freezing point of those films. | J.T.