But apart from the question of expense there are several important reasons why the blacksmith will find Dissolved Acetylene the best form of Acetylene for welding. Dissolved Acetylene is practically pure Acetylene. Its purity is as high as 98%, a quality of gas only commercially obtainable when generation, cooling, drying and purification by chemical means are carried out on a very large scale.

Adequate purification and cooling of gas within the compass of a small Acetylene generator is most difficult, if not impossible to obtain, and the larger the generator, of course, the less portable it becomes. The largest size of Dissolved Acetylene cylinder is easier to carry about than an Acetylene generating plant of much smaller capacity, and thus we come to the second important advantage of Dissolved Acetylene - its convenience and portability. The need for carbide and water supplies is eliminated- also the delay involved in preparation of plant, for the Acetylene is there, ready for use at a twist of the valve. A hand trolley (Fig. 234) can be supplied where required for transport of Acetylene and Oxygen cylinders, blowpipes, and all accessories for short distances.

Dissolved Acetylene is stored under pressure. The " ALDA " Blowpipe, which is specially designed for use with Acetylene under pressure, is so made as to take every advantage of this fact, with the result that it is possible at all times to maintain complete control of the mixture of the Oxygen and Acetylene in the blowpipe.

Fig. 234.

Where a blowpipe which includes an injector is used (and the injector type is essential with low pressure acetylene) this is only possible to a very approximate degree as there must necessarily always be some preponderance of Oxygen (under high pressure) in order to assist the flow of Acetylene (under low pressure). The maximum calorific value of the Oxy-Acetylene flame (6,500% Fahr.) is only attained where the two gases are correctly mixed prior to combustion, and this ideal condition is only practically possible by the use of both gases under high pressure, burnt at the tip of a blow-pipe, such as the " ALDA " Welding Blowpipe, designed especially for the purpose of maintaining correct mixture.

It should be noted that Acetylene Generating Plants of the workshop type must be housed in a special building licensed for the purpose by the local police authorities. Nothing of the kind is required in the case of Dissolved Acetylene which may be stored anywhere without risk.

In the case of small generating plants supplied at cheap prices it is necessary to emphasise the fact that such plants as these are totally inadequate to deal with the general range of work required in the repair of agricultural machinery. For example, a generating plant with a carbide capacity of, say, 9 lbs. will produce a maximum of 40 cu. ft. of Acetylene, but from such a generator it is impossible to obtain an hourly output of acetylene greater than half the capacity of the generator, i.e., 20 cu. ft. per hour; whereas the welding of 1/2in. steel requires not less than 30 cu. ft. per hour through the blowpipe. The consequence is that the strain upon the resources of the generator is so great that the gas is overheated and loses its natural character, a result of which the clearest possible evidence is immediately forthcoming in the very defective welding produced.

For welding repair work, therefore, the quality of materials is of the highest importance and the cost of obtaining a pure and efficient supply of Acetylene is negligible by comparison with the amount of damage which might otherwise occur.

The simplicity and efficiency of Dissolved Acetylene welding and metal-cutting equipment is such that a blacksmith, farrier, or wheelwright, with the knowledge of metal working which his experience has given him, will very quickly pick up the knack of handling the blowpipe to advantage and thus increase his business by a reputation for reliable work. (Messrs. Allen Liversidge, Ltd.)

Wireless Receiver Faults.

Wireless receivers may operate by means of a crystal only, or by means of valves, or by a combination of both, and as some form of aerial, an earth connection, headphones (or a loud speaker) may be used in common, the troubles that may arise with these parts are dealt with first.

No attempt is made here to deal with any particular form of circuit, these are extremely numerous, and it is assumed here that an efficient design is being used.