mnd of Potatoes, by the Jgency of Sulphuric Acid. 135 



ll>e experimentis, and by whose kindness 1 have been allowed 

 to operate in the Laboratory of the Royal Institution. 



The original experiment was made by boiling together 

 100 parts of starch, 400 parts of wafer, and one part of sul- 

 phuric acid, for 36 hours, on a slow fire, in a covered vessel, 

 adding from time to time water for that which boiled away : 

 towards the expiration of that lime some charcoal in pow- 

 der was put in ; and lastly, enough of carbonate of lime to 

 saturate the acid: the solution was then filtered, evaporated 

 to the consistence of a thick syrup, and put to crystallize ; 

 •which generally takes place in three days. In repeating 

 this experiment I got some starch not converted, which 

 was owing I believe to the heat not being sufficiently strong, 

 with the intention of shortening the time of boiling. I in- 

 creased the quantity of sulphuric acid (at the suggestion 

 of Professor Berzelius in a second trial) to 3 per cent. I 

 have also made trials with 4, 5, 6, and 8 per cent, of acid, 

 but they did not either increase the result, or shorten the 

 time of boiling, as much as I expected. I have also made 

 experiments with the starch of potatoes, in the same pro- 

 portions as that of wheat which I used in my first trials : 

 the only difference J could perceive between them was, that 

 the sugar was not so abundant from the potatoe starch, and 

 that it contained more c'lu^n^y niatter than the sugar ob- 

 tained from that of wheat. I observed that they do not 

 possess the property of sweetening liquids, at all equal to 

 the sugar from the juice of the cane. I have; not been able 

 to procure either of them sufficiently crystallized, to state the 

 diticrenceof either of them (if any) from each other, or from 

 any other sugar. Mv experiments at present are not suflli- 

 ciently complete to warrant my giving either a statement 

 of the quantity produced, or of the expense of the process ; 

 indeed this would be foreign to my first object, which wa^i 

 to repeat the experiment; but I am convinced it cannot be 

 an object at present in Britain. I am assured it was lately 

 in contemplation to adopt it on a large scale in the Russian 

 empire, as the price of cane sugar was increased so much, 

 and the supply was io uncertain, 



I shall not presume to give the rationale of this process 

 at present. I am ignorant of that advanced by the able dis- 

 coverer (M.Kirchhoff); but I must dissent from the opinion 

 given by M. Nnsse*, who thinks the sulphuric acid is de- 

 composed. 1 have weighed the quantity of lime it required 

 to saturate the acid used in the experiments; and also of 



• See Journal de Phi/tiqut Mi-.rs 1815, page 199, &c. which did nolarrive 

 iA this cuuatry until after these experinienti w«'e inude. 



I 4 that 



