8o 
PRACTICAL PHOTO-MICROGRAPHY. 
through ; in the mixing jet both the coal gas—or 
hydrogen—and the oxygen are forced into the jet at 
some pressure, mix in a “ chamber ” near the nozzle, 
and emerge from the nipple mixed. In short, we have 
to do with two varieties of blow-pipe making a piece of 
lime incandescent over a certain area of its surface. 
The mixing jet being more powerful, we use with it a 
lime as hard as we can procure, and best of all is a 
piece of true limestone, which may be got under the 
name of u Nottingham ” lime. The limes are turned, 
sometimes very roughly, to the shape of a cylinder, the 
“ lime-pin ” of the jet passes up through the middle of 
the cylinder, and so the lime is kept in position with 
relation to the nipple of the jet. The mixing type of 
jet is superior to the other, not only for its greater 
brilliance, but also because the point of light is smaller 
and of better actinic quality in the mixing than in the 
blow-through jet. For the blow-through jet we require 
gas from the main, and oxygen under some pressure. It is 
easy to make oxygen gas, and to put it under pressure 
in a gas-bag, but nowadays this gas can so easily and 
so cheaply be procured in metal cylinders that probably 
no one thinks of making his own oxygen. The Brin 
Oxygen Co. supply oxygen in cylinders ; as the gas is 
under very great pressure a small cylinder holds a large 
quantity of gas. 
For the mixing jet we require both oxygen and 
hydrogen under pressure, and the hydrogen—or coal- 
gas—is also supplied in cylinders by the same company. 
But the light of a mixing jet is so powerful that one 
