DR. E. FRANK land’s RESEARCHES ON ORGANO-METAELIC BODIES. 
2()0 
Fig. 1. 
.4 
at the bottom, and welded in one piece by the steam-hammer. This cylinder is 
18| inches long, finch in thickness, and 3 inches internal diameter; it is furnished 
at top with a flanch, B, B, if inch broad and f inch 
thick, its upper surface turned true, and having an internal 
annulus sunk inch below the level of the surrounding 
surface. The cap of the digester, C, C, is made to fit upon 
this flanch, with which it corresponds in thickness and dia- 
meter ; it is furnished with a projecting face finch deep, 
fitting the mouth of the cylinder exactly. Within the circle 
of this projecting face, the cap is perforated by two aper- 
tures, into one of which is securely fixed the cast-iron tube 
dd, closed at the bottom, 6 inches long and finch internal 
diameter, forming a mercury bath for the reception of a 
thermometer. The other aperture, which is bouched with 
brass, serves as the bed of the safety valve e, which con- 
sists of a piece of brass wire f inch diameter, slightly flat- 
tened on two sides and furnished with a head accurately ground to the surface of the 
cap : pressure is applied to this valve in the usual manner by the lever and weight f,g. 
Both the flanch and cap are perforated by four holes for the reception of four screw 
bolts finch in diameter, which are inserted from below, and work into nuts that can 
be tightly screwed up by a lever key. The whole of the pressure produced by these 
screw bolts is made to take effect exclusively upon the surface of a leaden washer f inch 
thick, placed in the sunken annulus above mentioned ; and thus the apparatus is made 
perfectly impervious to gases and vapours, even under the enormous pressure of more 
than 100 atmospheres. Before use, this vessel was proved, by being two-thirds filled 
with water, and then gradually heated up to the melting-point of lead. It has since 
been exposed with impunity to a still more severe test ; for on one occasion, when 
charged with water and a glass tube filled with iodide of methyl, at a temperature 
of 200° C. the glass tube burst, and such was the tension of the iodide of methyl 
vapour, that the safety valve was instantaneously expelled, and the heavily loaded 
lever thrown completely over. In this digester, volatile liquids enclosed in glass 
tubes of large dimensions and moderate thickness of glass, may be exposed to any 
temperature below redness with safety. I prefer to use water in the digester, but 
other and less volatile liquids may of course be substituted if desired: in most expe- 
riments, however, it is important that the pressure upon the exterior of the glass tubes 
should not be much less than that in their interior, and this condition is generally 
secured l)y the employment of water in the apparatus. 
The second digester is made of wrought copper and is of smaller dimensions, being 
especially designeil for the preparation of large quantities of organo-zinc compounds, 
without the intervention of glass tubes. It consists of a wrought copper tube. A, A 
(fig. 2), 18 inches long, 1^ inch internal diameter, and ^ inch in thickness, drawn 
