S. W. Johnson on the estimation of Carbonic Acid. 113 
When properly executed the process gives extremely accurate 
results ; a slight change of temperature or of atmospheric pres- 
sure between the two weighings of course greatly impairs the 
results or renders them worthless. Since the apparatus usually 
rises a little in temperature during the solution of the carbo- 
nate, it is better, as soon as the substance is decomposed, to 
stopper the CaCl tube and let the whole stand fifteen minutes, 
then to connect as before with the CO generator and pass dried 
O, for a minute, and finally to stopper again and bring upon 
the balance. In seven analyses of pure calcite in quantities 
_ ranging from 0°5 to 0-9 grm., the writer obtained the following 
percentages of carbonic acid, viz: 44:07, 44-07, 43°98, 44-01, 
— 44-04, 44-11, 
44°16 ; calculation requires 
In case of alkali-carbonates which absorb carbonic acid gas, 
it is necessary to modify the apparatus. Instead of the light 
flask a we may employ a small bottle of thick glass and wider 
mouth, and a thrice-perforated aed stopper. Through the 
third orifice pass ‘a narrow tube 3 to 4 inches long enlarged 
below to a small bulb to contain ou carbonate. This bulb 
_ must be so thin that on pushing down the tube within the bot- 
_ tle, it shall be easily crushed to pieces against the bottom of the 
latter. The carbonate is weighed into the bulb-tube, the lat- 
_ ter is wiped clean, down to the bulb, corked and fixed in the 
: poppet. The apparatus is filled as before with CO, and 
weighed. Then the bulb is broken and the process finished as 
before described. In three estimations on carbonate of soda 
_ the writer found 41°54, 41-64 and 41°58 per cent of CO,. - 
_ culation requires 41°51 per cent. 
2. ve se construction of Bunsen’s scrote 
es of gc inh pipe in the garret flue was attached a third 
Jeaden fall-pipe of 4 inch bore which passed down to the cellar 
bottom with a vertical height of more than 40 feet, and there 
tered into a drain pipe. The supply-pipe and air-pipe were 
_ Am. Jour. Sc1.—Seconp Senigs, Vou. XLVIII, No. 142.—Juxy, 1869. 
8 
