The insulation of buildings, more particularly those used for acetylene generators, is of vital importance from a point of safety. Perfect insulation is almost impossible, but a good insulation can be had.

Messrs. Lamb and Wilson, of Cambridge University, in a paper communicated to the Royal Society by Prof. Ewing, F.R.S., in 1899, have published the results of tests made by them as follows : -

The Cartvale flake charcoal is thus superior in its insulating value as compared with the other materials, while, owing to its lightness, much less weight of it is required to fill a given space, and yet give better insulation.

It may be remembered that the amount of heat to be overcome is not to be measured by the cubical contents of the insulating room, but by the amount of square or wall surface exposed to the heated exterior.

1 Silicate Cotton has been found practically to be out of the question, as it breaks down easily, leaving open spaces, or falls down to powder.

2 Felt absorbs damp very quickly, and, owing to its composition, draws up water by capillary attraction, thus spoiling it as a non-conductor and rotting it; in addition, it is apt to breed vermin.

3 The lump charcoal was first broken into pieces about half-inch cube.

C. High-pressure Oxy-acetylene Welding Plant.

In this type of welding plant the acetylene is used in a compressed state, similar to that of the oxygen.

Like all other gases, acetylene is capable of compression and liquefaction, and when used in this form is called "dissolved acetylene," and known abroad under the name of "acetylene-dissous." It is produced as follows: -

The acetylene, generated in the usual way, is thoroughly washed and subjected to no less than five different processes of purification, and dried. It is then compressed and passed into the ordinary steel cylinders for storage. The compression is carried out by a double-acting pump, which compresses it in two stages, as the process is accompanied by an evolution •of much heat, which might cause the gas to explode during the operation; but since the pump is fitted with two cylinders, the acetylene can be cooled after the first compression.

The cylinders, of any size, are filled with a porous solid material in the form of a charcoal cement, and charged to about 43 per cent. of their capacity with acetone, thus leaving 37 per cent. of the space for expansion which takes place, making an explosion in the cylinder an impossibility. Acetone is a liquid, which has the peculiar property of absorbing twenty-five times its own volume of acetylene at atmospheric pressure and 15° C, and will continue doing this for every atmosphere of pressure that is applied to the gas. The quantity of acetone in the cylinders is so regulated that they contain ten times their own volume of acetylene for every atmosphere of pressure. The gas in the cylinders sent out by the company is compressed to ten atmospheres, so that they contain one hundred times their own volume of acetylene.

The safety of the system has been demonstrated in the fullest possible manner to the Home Office, in consequence of which the Secretary of State for the Home Department, in April, 1901, issued an order recognising the safety of dissolved acetylene, and authorising its use according to the process adopted by the Acetylene Illuminating Company on condition that (1) the porous material used is to be exactly similar to the sample deposited with the Home Office, (2) all cylinders are to be tested according to certain rules laid down, (3) certain technical details in the manufacture of the gas and charging of the cylinders be carefully observed, (4) that every facility be given to the Government inspectors to inspect the company's plant and method of working, and (5) every cylinder or container to bear the name of the Acetylene Illuminating Company, Limited, and be marked "Acetylene compressed into porous substance exempted by order of Secretary of State, dated 10th April, 1901."

For autogenous welding in conjunction with oxygen dissolved acetylene offers many advantages, particularly in places inaccessible to other welding plants or systems, such, for instance, as the hold of a ship.

The gas being chemically pure is always cool and dry, and at a steady pressure most suitable to ensure maximum of efficiency. The consumption of the gas is shown by the gauge, so that the quantity remaining in the cylinder is known at a glance.

Cylinders for Acetylene-Dissous.

High-pressure oxy-acetylene welding plant consists of the acetylene cylinder; the oxygen cylinder ; the regulator and safety device, fitted with two pressure gauges for the acetylene cylinder; and similar ones for the oxygen cylinder; one or more high-pressure blowpipes; two lengths of rubber tubing; spectacles; and cylinder key.

When working high-pressure plant, first examine cylinder valve to see if same is clean. The governor can then be screwed into the valve (this is a left-hand thread), making sure the joint is sound. The same thing must be done with the oxygen cylinder. In this case the thread of the governor is right hand.

The regulators for the acetylene cylinders are painted red and have left-hand connections to fit the valve in the acetylene cylinders; the regulators for the oxygen cylinders are painted black and have right-hand connections. This is done so as to make it impossible for the wrong regulators to be used with either gas, otherwise they are identical. The pressure can be adjusted by unscrewing the screw R (Fig. 8, p. 43) for low pressure, or by screwing down R for high pressure. The indicator M indicates the pressure of delivery as set by E. The maximum pressure at which the regulator will work is marked by a red line on the indicator M, and if this pressure is exceeded (by screwing R too heavily) a safety-valve S will open and relieve the excess pressure. The tap H for controlling the supply is a convenience which the safety-valve S renders possible. N is the delivery nozzle, and F is a gauge for registering pressure of gas in cylinder.

Then connect the outlet of the acetylene governor, by means of rubber tubing, to the nozzle on the blowpipe, stamped A, and the oxygen governor to the nozzle on blowpipe marked 0. Care should be taken to bind the rubber at all joints with wire.

Then see that the milled head screw on outlet of each governor is open, and that tap R on top of each governor is free from the governor springs (this is so when tap R is nearly out of the socket). Then turn on the gas at both cylinder valves; no gas will pass to the burners if the tap R on the regulators is free. Screw down the tap R on top of the acetylene governor until pressure on outlet gauge shows 3 to 3 1/2 lbs.; light the burner, then screw down tap R on the oxygen governor until the necessary white tip on the burner is obtained, gradually increase the pressure on the acetylene until it reaches 5| lbs. Do not do this in one step, but work the two governors alternately.