80 GuY^ on preserving Microscopic Objects in Tubes. 
of lead, is to be preferred. I may add_, tliat it is desirable to 
procure tubing recently drawn, and not such as has been 
lying for a long time in the glass-house contracting dust. 
The tubing is very cheap, sold by the pound, and the ultimate 
cost of the minute tubes in which the specimens are mounted 
would be some small fraction of a penny. 
It will be seen that each tube thus drawn out consists of a 
small central tube able to receive one or two microscopic 
specimens, and of a larger portion at each end available as a 
funnel for the introduction of the specimen itself. 
When we wish to obtain a sublimate within the narrow 
portion of the tube, and the substance to be operated 
upon does not sublime at a low temperature, we first intro- 
duce the object through the large open mouth of the tube 
into the commencement of the narrowest portion; we then 
seal the tube in the flame of the lamp, and thus form a 
retort in miniature. We now shake the object into the 
sealed end of the tube-retort, heat the end, and obtain the 
sublimate in the narrow portion of the tube. The small 
tube, being drawn off and sealed on both sides of the sub- 
limate, may now be mounted for the microscope. I send 
round a tube which has been dealt with in this manner. A 
piece of copper-foil coated with the metal arsenic by Reinsch's 
process has been introduced, sealed up, and heated, and a 
crystalline ring of arsenious acid has been sublimed into the 
narrow portion of the tube. The crystalline texture of this 
ring may be seen by the lens, but it is clear that for thorough 
examination of the sublimate, and the identification of the 
crystals as those of arsenious acid, the microscope must be 
brought into play. This specimen, then, will suffice to prove 
the necessity of using the microscope. 
In those cases where the substance to be operated on sub- 
limes under a comparatively low temperature, we must either 
employ a tube with a longer extremity, so that the substance 
may not be unduly heated in the act of sealing the tube, or 
we must first seal the tube at one end, dry it carefully by 
passing it repeatedly through the flame of the lamp, and 
then so contrive to introduce the substance to be operated on 
through the open end of the tube, as not to soil it in its passage. 
To effect this, the tube must be held in a vertical position, 
and the substance to be heated must be dropped in in very 
small fragments. 
I have hitherto spoken only of round tubes drawn out from 
round tubing ; but I may now add that the oval tubing sold 
by the glass-maker may be treated in every respect in the 
same way as the round tubing; and that when drawn out in 
