of simple alimentary Substances, $c. 103 



presently, the same essential composition, but the starch dif- 

 fering from the sugar by containing minute portions of other 

 matters, which, we may presume, prevent its constituent par- 

 ticles from arranging themselves in the crystalline form, and 

 thus cause it to assume totally different sensible properties*. 



Wheat Starch. — The most perfect form of the amylaceous 

 principle is undoubtedly that derived from wheat. This has 

 been analysed by different chemists with very different results. 

 MM. Gay Lussac and Thenard state that they found it to con- 

 tain as much as 43'55 per cent, of carbon ; while Dr.Ure in- 

 forms us that he only found 38*55 per cent. The following 

 observations will sufficiently explain these differences. 



A very fine specimen of wheat starch, which had been pre- 

 pared expressly at my desire without the addition of the co- 

 louring matter commonly added to the starch of commerce, 

 and which had been kept in a dry situation for many months, 

 was found, in the ordinary columnar form in which it usually 

 occurs, (abstracting foreign matters,) to consist of 



Carbon 37*5 



Water 62-5 



One hundred parts of the same specimen reduced to a state 

 of fine powder, and subjected to a temperature between 200° 

 and 212°, for the space of twenty hours f, lost, m a mean of 



* When this subject first occupied my attention many years ago, I was 

 at a loss to form any notion of the modus operandi of these minute admix- 

 tures of foreign bodies, except the mechanical one mentioned in the text, 

 viz. that they operated by being interposed, as it were, among the essential 

 elements of bodies, and thus by weakening or modifying their natural affi- 

 nities. But the admirable paper, published by Mr. Herschel, in the Philo- 

 sophical Transactions for 1824, " On certain motions produced in fluid con- 

 ductors when transmitting the electric current," appeared to throw an en- 

 tire new light on the subject. The facts brought forward in this paper are of 

 the most important kind, and seem to me to be evidently connected with a 

 principle of a more general character, which when completely developed, 

 will lead to the most unexpected results. " That such minute proportions 

 of extraneous matter," says Mr. H. " should be found capable of commu- 

 nicating sensible mechanical motions and properties of a definite character 

 to the body they are mixed with, is perhaps one of the most extraordinary 

 facts that has yet appeared in chemistry. When we see energies so intense 

 exerted by the ordinary forms of matter, we may reasonably ask what 

 evidence we have for the imponderability of any of the powerful agents to 

 which so large apart of the activity of material bodies seem to belong?" 



Any substance may be supposed capable of performing the part of a mer- 

 organizing body ; but, in a certain point of view, ivater appears to consti- 

 tute the first and chief, at least in organized substances. 



1 1 have reason to believe from other experiments that six or eight hours, 

 or even less, of steady exposure to the boiling temperature, will sometimes 

 reduce both starch and arrow root, and even gum, to this state of desicca- 

 tion. 



two 



