4i 8 Baker. — - Quantitative Experiments on 
containing certain quantities of methyl alcohol and organic acids as im- 
purities. These impurities were absorbed by the potash through which the 
vapour was passed, as it entered the bell-jar (Text-fig. i). 
( b ) The air was passed over solid paraform, at known temperature. 
This is a polymer of formaldehyde, which yields the aldehyde in the form 
of pure vapour on heating. 
(c) The air was passed through a ‘ diffusion bulb ’ containing formalin. 
This little apparatus (Text-fig. 3) was used for introducing more volatile 
vapours, such as carbon disulphide, 
into the air-current when required 
(see p. 441). The bulb was filled with 
the liquid (in this case formalin) by 
the method of heating and cooling, 
and then the air-current passed along 
the glass-tube, sealed into the open- 
ing of the capillary, T-piece fashion. 
The air carries with it the traces of 
formaldehyde vapour which diffuse 
through the capillary, thus leaving 
its vapour pressure at the opening of 
the capillary always zero. This keeps the amount of vapour diffused out 
constant at a given temperature, the driving pressure being always equal 
to the vapour pressure of formaldehyde at that temperature. 
The Air Outlet . 
The air passed out of the bell-jar through a long bent glass tube, 
opening above the liquid in the bath and passing under the rim of the bell- 
jar through this liquid. In the cultures where carbon dioxide was excluded, 
the air passed out from the bell-jar through a caustic potash bubbler, to 
prevent possible access of carbon dioxide by a back rush of air ; and where 
formaldehyde or acetic aldehyde was the vapour, this was cleared out of the 
air by bubbling through aniline. The pump was, however, about seven 
metres from the bell-jars, so that contamination of the air-stream was not 
probable. 
Diffusion Bulb 
Experimental Results. 
Effect of Formaldehyde Vapour in the Air. 
Amount of Formaldehyde in the Air-current. 
Determined in a separate experiment by weighing the diffusion bulb, 
bubbler, or U-tube, containing the formalin or paraform used as the source 
of formaldehyde, before and after the passage of a known volume of dry 
