ufacturers and others have long since learned that when glass
is in question not only are fused joints made as easily as others, but
that they afford the only reliable form of joint. An experimenter who
uses flint glass, has a little experience, an oxygas blow-pipe and a
blowing apparatus, will prefer to make his joints in this way, simply
from the ease with which it may be done. When it comes to making a
tight joint between glass and other substances the problem is by no
means so easy. Thus Mr. Griffiths (Phil. Trans. 1893, p. 380)
failed to make air-tight joints by cementing glass into steel tubes,
using hard shellac, and the tubes fitting closely. These joints were
satisfactory at first, but did not last; the length of the joint is
not stated. The difficulty was finally got over by soldering very
narrow platinum tubes into the steel, and fusing the former into the
glass.

Mr. Griffiths has since used an alloy with success as a cement, but I
cannot discover what it is made from. Many years ago Professor Hittorf
prepared good high vacuum tubes by plugging the ends of glass tubes
with sealing wax merely, though in all cases the spaces to be filled
with wax were long and narrow (Hittorf, Pogg. Ann. 1869, Sec. 5,
English translation, Phys. Soc. p. 113). Again, Regnault
habitually used brass ferules, and cemented glass into them by means
of his mastic, which can still be procured at a low rate from his
instrument-makers (Golan, Paris). Lenard also, in his investigations
on Cathode Rays (Wied. Ann, vol. li. p. 224), made use of sealing
wax covered with marine glue.

Surely in face of these facts we must admit that cement joints can be
made with fair success. I do not know the composition of M.
Regnault's mastic, but Faraday (Manipulations, Sec. 1123) gives the
following receipt for a cement for joining ferules to retorts, etc:

Resin 5 parts.

Beeswax 1 part.

Red ochre or Venetian red,
finely powdered and sifted 1 part.

I believe this to be substantially the same as Regnault's mastic,
though I have never analysed the latter.

For chemical work the possibility of evolution of gas from such a
cement must be taken into account, and I should certainly not trust it
for this reason in vacuum tube work, where the purity of the confined
gas could come in question. Otherwise it is an excellent cement, and
does not in my experience tend to cr