18h5.] Conversion of Starch into Sugar. 429 
Method of conducting my Experiment. 
In the preceding analyses I made use of the following method, 
which I employ in the analysis of gummy and woody bodies that 
contain very little or no azotic gas. I reduce the vegetable body to 
as fine a powder as possible, mix it with 50 times its weight of 
silicious sand, and put it intoa glass tube bent in the middle at a 
right angle, close at one end, and furnished at the other with an 
iron stop cock. This tube is about a metre (39°37 inches) in 
length, and its width is such, that it is capable of containing rather 
more than 200 cubic centimetres (12°2 cubic inches) of gas. FE 
weigh the vegetable substance by the way of substitution, in the 
tube itself, by means of a balance, which, when loaded, turns by 
the addition of one milligramme (0°015 gr.) The air is then ex- 
tracted from this tube by means of the air pump; it is filled with 
oxygen gas, the stop cock is shut, and all its joints are covered 
over with mastich, or it is surrounded by a column of mercury 
during the burning of the vegetable matter, in order to be certain 
that no gas makes its escape while it is expanded by heat: for: the’ 
stop cock, which incloses a portion of gas, is not always able to 
withstand the compression or dilatation which takes place within, 
which frequently acts as a kind of valve. 
The stop cock being thus secured, I heat that part of the tube 
with which the vegetable body is in contact, to an obscure red; 
and for this purpose I employ a spirit lamp, which gives a flame at 
least one decimetre high (3°937 inches), and at least of such a’ 
diameter as to surround the whole circumference of the tube. 
Liquid and sooty matter speedily disengages itself, and is depo- 
sited in a neighbouring part of the tube, whieh is kept cool by 
being surrounded with moist paper. I afterwards heat this part of 
the tube to redness. The vegetable matter burns, and is partly 
volatilized and condensed in another part of the tube. This new 
portion is heated to redness in its turn, I go on in this manner, 
heating the condensed portion a great many times in succession, 
till the decomposition appears to be complete, and the liquid fe- 
maining to be nothing else than pure transparent water. 
To measure the alteration of the volume, which the gas has 
undergone during the combustion, I fill a graduated tube one deci- 
metre in length, and furnished with an iron stop cock at each end, 
with mercury and with oxygen gas, fix it on the first tube, plunge 
the end of it under mercury, and open both the stop cocks, which 
establishes a free communication between the two tubes, and ob- 
serve the increase or diminution of gas which has taken place. ‘Fo 
get the gas out of the tube, | screw upon both the tubes a balloon, 
furnished with a stop cock, and filled with mercury. ‘The mercury 
runs into the tube, and the gas makes its way into the balloon. The 
quantity of it is sufficient to make four eudiometrical experiments 
on its nature, 
In order to determine whether the vegetable substance subjected 
