An examination of the various methods existing for the production and liquefaction of combustible gases, of their easy application and economical advantages, and of the phenomenal advance during the last three years in their adaptation to an immense variety of metallurgical and engineering operations, which have hitherto been carried out under less favourable conditions, proves that compressed gases have become an indispensable factor in almost every branch of industry.

The small space available for this important subject will be limited to a description of welding and cutting metals by means of combustible gases as well as the application of electric welding.

Recent investigation, personally made by the author in various countries, has proved that welding is being used to a far greater extent than is generally known.

Welding is, however, associated with and dependent upon many different factors, all of which must be simultaneously considered to enable even the most skilful workman to produce satisfactory results.

A general description, therefore, of the various and distinct methods, their suitability and selection for different operations, together with a collection of results and tests obtained, in many cases intuitively illustrated, will, it is hoped, assist in the advance in technical knowledge and lead to gradual accumulation of practical experience so necessary in every new industry.

There are, however, many important points open for investigation, amongst which may especially be mentioned the effects of the different gases and their mixtures, as well as of the extreme temperatures, and their physical, chemical, and biological action upon the metals.

It would also be of great importance to find some means whereby an inferior weld, sheltered under a smooth and perfect surface, obtained by the use of gases of inferior purity or by unskilled labour, could be detected so as to render that safety which, in some branches of the industry, is of vital importance.

By the introduction of liquefied and compressed gases a new industry of great importance and almost unlimited possibilities has been created. That which has already been done, although of great extent, constitutes, however, merely an indication of what really can be accomplished in this vast industrial field opened up for investigation and development, resulting, as it may, in the entire revolution of present working methods in engineering and metallurgy.

In conclusion the author gladly expresses his indebtedness to the Editors of the Technical Press at home and abroad, amongst which may specially be mentioned the Electrical Times, Marine Engineer and Naval Architect, and many others, as the Royal Society of Arts; Institute of Marine Engineers ; A.G.f. Aluminium Schweissung; British Oxygen Co., Ld.;

Electric Welding Co., Ld.; Garuti & Pompilj; Hugo Helberger, G.m.b. H.; and Stewarts and Lloyds, Ld., who have contributed information and kindly allowed the use of illustrations.

The author also desires to acknowledge the courteous manner in which he was received by the owners and chief engineers of many of the leading engineering works at home, as well as in Belgium, France, Italy, Austria, and Germany, and their readiness to show and explain everything that was desired.

L. A. GROTH.

London, 10, Gratton Road, West Kensington, 1908.