The leading fact of the vehement combination and complete union of acid and alkali readily suggested a fit form for the particles of the latter class of substances. 'This effect,' Lemery adds, 'may make us reasonably conjecture that an alkali is a terrestrious and solid matter whose forms are figured after such a manner that the acid points entering in do strike and divide whatever opposes their motion.' And in a like spirit are the speculations in Dr. Mead's _Mechanical Account of Poisons_ (1745). Thus he explains the poisonous effect of _corrosive sublimate_ of mercury by saying[8\6] that the particles of the salt are a kind of lamellæ or blades to which the mercury gives an additional weight. If resublimed with three-fourths the quantity of mercury, it loses its corrosiveness, (becoming _calomel_,) which arises from this, that in sublimation 'the crystalline blades are divided every time more and more by the force of the fire:' and 'the broken pieces of the crystals uniting into little masses of differing figures from their former make, those cutting points are now so much smaller that they cannot make wounds deep enough to be equally mischievous and deadly: and therefore do only vellicate and twitch the sensible membranes of the stomach.' [Note 8\6: P. 199.] 7. Among all this very fanciful and gratuitous assumption we may notice one true principle clearly introduced, namely, that the suppositions which we make respecting the forms of the elementary particles of bodies and their mode of combination must be such as to explain the facts of crystallization, as well as of mere chemical change. This principle we shall hereafter have occasion to insist upon further. I now proceed to consider a more refined form of assumption respecting the constitution of bodies, yet {10} still one in which a vain attempt is made to substitute for the peculiar idea of chemical composition a more familiar mechanical conception.