ON POTATO SUGAR. 
59 
tinned until a small portion of the liquid, neutralized with 
chalk and filtered, gave no precipitate with a solution of 
diacetate of lead, which occupies in general from five to six 
hours. 
The liquid was then neutralized with chalk, boiled and fil- 
tered — the filtered solution digested with animal charcoal to 
deprive it of what little colour it had acquired, again filtered, 
and the washings of the charcoal added to the solution, which 
was then evaporated in a water-bath to the consistence of 
honey, and placed in a warm situation for three or four 
days, when the whole solidified into a crystalline mass of 
grape sugar, having a perfectly sweet taste, unaccompanied 
by any bitterness, while that made with sulphuric acid had 
a nauseous bitter taste, and crystallized with much greater 
difficulty. 
In addition to the superiority of the product obtained by 
this process, we have the great advantage of being able to 
ascertain when the whole of the starch has been converted 
into sugar, by its giving no precipitate with a solution of 
diacetate of lead, which shows that the dextrine, into which 
the starch is first converted has undergone its complete 
change, and enables us to avoid unnecessary boiling, which 
destroys its tendency to crystallize, an advantage not af- 
forded by the use of sulphuric acid, because the sulphate of 
lime retained in solution (however small in quantity) pre- 
cipitates sulphate of lead, which, though very different in 
appearance to the compound of gum and oxide of lead, 
might be mistaken for it in small quantities. 
Since adopting the above process, I find that Mr. Gra- 
ham, in his Elements, suggests the use of 1 -200th part of 
oxalic acid, but I have not been able to succeed with any- 
thing like so small a quantity. 
A mixture, in the proportions prescribed by Mr. Graham, 
was boiled for fourteen hours and a half ; but the liquid, 
though much discoloured, was not even made limpid, far 
