130 Mr. C. T. Coathupe on certain 



tion of the remainder, while the other lead compound loses 

 five equivalents of water at 200°. 



The constitution of these substances may be viewed in 

 a somewhat different light. Water, existing as such, com- 

 bined with any substance allied to starch, either basic or con- 

 stitutional, as supposed above, is never known to be so inti- 

 mately combined with the substance as to be incapable of 

 displacement by oxide of lead, especially under such a favour- 

 able circumstance as the presence of free ammonia. When 

 substitution appears impossible, it is therefore reasonable to 

 conclude that the water, if it exists at all, is neither basic nor 

 constitutional, but is essential to the substance itself. 



The remarkable circumstance of inulin giving off at one 

 time three equivalents of water, and not at another, under ap- 

 parently the same circumstances, suggests the idea that two 

 inulines exist, having the same composition, but one con- 

 taining water capable of displacement, which the other does 

 not. This substance has, indeed, been obtained by chemists 

 in two different physical states, gummy and pulverulent (al- 

 though I have never obtained out the former dry) ; and I 

 would suggest the probability of these having the constitutions 

 above-mentioned, that is, that one is C 24 H 21 21 , and the other 

 C 24 H 18 18 -f 3 HO ; a feeble but unknown cause being suf- 

 ficient to convert one into the other. 



This is not a singular instance of a double constitution. 

 In fact, the only satisfactory means of accounting for dimor- 

 phism, is by supposing a difference in the constitution of the 

 same substance at one time to that which it possesses at 

 another, the ultimate composition continuing the same. In 

 diabetic sugar, also, we have reason to suspect a double con- 

 stitution, the descriptions of this substance by various authors 

 being, as is well known, highly discordant. Some identify 

 it with starch sugar; others, on the contrary, describe it as 

 a peculiar substance. This is an interesting and very exten- 

 sive inquiry, and would probably throw light on some of the 

 cases of isomerism still unexplained. 



University College, London, 

 May 16, 1840. 



XX. On certain Effects of Temperature. By C. T. Coat- 

 hupe, Esq. 

 To the Editors of the Philosophical Magazine and Journal. 

 Gentlemen, 

 TLTAVING, from the nature of my occupations, an excellent 

 -*■ * laboratory for observing the effects of temperature, I beg 



