Front Page Titles (by Subject) DVII: TO M. DUBOURG - The Works of Benjamin Franklin, Vol. VI Letters and Misc. Writings 1772-1775
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DVII: TO M. DUBOURG - Benjamin Franklin, The Works of Benjamin Franklin, Vol. VI Letters and Misc. Writings 1772-1775 
The Works of Benjamin Franklin, including the Private as well as the Official and Scientific Correspondence, together with the Unmutilated and Correct Version of the Autobiography, compiled and edited by John Bigelow (New York: G.P. Putnam’s Sons, 1904). The Federal Edition in 12 volumes. Vol. VI (Letters and Misc. Writings 1772-1775).
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TO M. DUBOURG
London, 1 June, 1773.
I wish, with you, that some chemist (who should, if possible, be at the same time an electrician) would, in pursuance of the excellent hints contained in your letter, undertake to work upon glass with the view you have recommended. By means of a perfect knowledge of this substance, with respect to its electrical qualities, we might proceed with more certainty as well in making our own experiments, as in repeating those which have been made by others in different countries, which, I believe, have frequently been attended with different success on account of differences in the glass employed, thence occasioning frequent misunderstandings and contrariety of opinions.
There is another circumstance much to be desired with respect to glass, and that is, that it should not be subject to break when highly charged in the Leyden experiment. I have known eight jars broken out of twenty, and, at another time, twelve out of thirty-five. A similar loss would greatly discourage electricians desirous of accumulating a great power for certain experiments. We have never been able hitherto to account for the course of such misfortunes. The first idea which occurs is, that the positive electricity, being accumulated on one side of the glass, rushes violently through it, in order to supply the deficiency on the other side and to restore the equilibrium. This, however, I cannot conceive to be the true reason, when I consider that, a great number of jars being united, so as to be charged and discharged at the same time, the breaking of a single jar will discharge the whole; for, if the accident proceeded from the weakness of the glass, it is not probable that eight of them should be precisely of the same degree of weakness, as to break every one at the same instant, it being more likely that the weakest should break first, and, by breaking, secure the rest; and again, when it is necessary to produce a certain effect, by means of the whole charge passing through a determined circle (as, for instance, to melt a small wire), if the charge, instead of passing in this circle, rushed through the sides of the jars, the intended effect would not be produced; which, however is contrary to fact. For these reasons, I suspect, that there is, in the substance of the glass, either some little globules of air, or some portions of unvitrified sand or salt, into which a quantity of the electric fluid may be forced during the charge, and there retained till the general discharge; and that the force being suddenly withdrawn, the elasticity of the fluid acts upon the glass in which it is enclosed, not being able to escape hastily without breaking the glass. I offer this only as a conjecture, which I leave to others to examine.
The globe which I had that could not be excited, though it was from the same glass-house which furnished the other excellent globes in my possession, was not of the same frit. The glass which was usually manufactured there, was rather of the green kind, and chiefly intended for drinking-glasses and bottles; but, the proprietors being desirous of attempting a trial of white glass, the globe in question was of this frit. The glass not being of a perfect white, the proprietors were dissatisfied with it, and abandoned their project. I suspected that too great a quantity of salt was admitted into the composition, but I am no judge of these matters.