It should be quite clear that the condition of uneven internal stress which may result in the season-cracking of brass articles is not a product of rolling mill work, nor a quality of the brass as such. It arises as the strip or sheet is made up, and by reason of working strains which often cannot be avoided. It is thus most desirable that both its causes and the possibility of its removal, should be understood. Those brasses containing the lower percentages of copper, namely, 63% and 67%, are mostly used for press operations where the thickness of the finished article is similar to that of the original strip. The deformation is carried out with press tools, and the folding or crinkling of the metal is prevented by the use of a pressure plate. The requirements of a metal for these press operations are cleanliness, smoothness of surface, corned annealing, and uniform thickness. A frequent source of failure in press operations arises at the forming of the first product from the blank. The damage caused at this operation generally consists of a local thinning of the metal, which does not reveal itself until a subsequent operation is performed, when fracture may result. Though frequently put down to the operation at which fracture actually occurs, and also to the metal, such failures should be attributed to a weakening of the metal by overwork at the previous operation.

Where it is required to reduce the thickness of the metal considerably at the various operations of manufacture, then a higher percentage of copper than is used for pressings is advisable, and the alloys containing from 68% to 72% of copper are most generally used. These so-called " cartridge metals " find extended application not only for the manufacture of munitions of war, but also for any purpose where ductility is a necessary property, combined with considerable strength.

As the copper content is raised still further, the properties of the brasses approach nearer and nearer to those of pure copper, which means that the hardening effect of cold-work becomes less marked, the strength becomes reduced, and the red copper-colour more pronounced. The softening and melting point of the brasses aiso increases with copper content. With the lower percentages of copper, hard-soldering or brazing is difficult, unless expensive silver solders be used. With the alloys richer in copper, from about 73% upwards, brazing can be carried out by means of the cheaper zinc-rich brasses. The change in colour as the copper content increases is a valuable property made use of by jewellers and others, where artistic bronze effects are required. Quite a small percentage of zinc in copper brings about a considerable modification in properties, the 97/3 alloy, so far as annealing is concerned, more nearly approaches cart ridge brass than copper. The ductility of such an alloy is considerable, and, therefore, for many small products such an alloy has certain advantages over pure copper. Perhaps one of the chief advantages to be gained from adding a small quantity of zinc to copper is the removal of any risk of " gassing" during annealing.

For certain bronzing operations by means of sulphide solutions, even a small percentage of zinc in the copper prevents such satisfactory results being obtained as when pure copper is used, hence the practice in art metal finishing of giving to brass articles a thin deposit of electro copper, so that, whilst the article has the strength of brass, it can be given a finish only satisfactorily applicable to copper.

The range of tensile strength of cold rolled brasses is from about 15 to 15 tons per square inch, the range of ductility from 3% to 70% elongation, the colour ranges from bright yellow through warm orange up to the red of copper.

Whatever the composition or properties of a brass there are some cardinal points that must be observed. The metal should be kept clean, and only go forward to pressing or drawing operations in a perfectly clean, lubricated state. Intermediate anneals should not be carried out at too high a temperature, or for too long a time. The annealing temperature of 650° need never be exceeded, and the time not be longer than required for the product to attain such a temperature. This specially applies to thin products which rapidly attain to the temperature of the muffle. Products in intermediate stages of manufacture should not be left lying about for long periods in a hard condition, otherwise trouble is liable to arise through season-cracking. If it is necessary to store products at some intermediate stage, they should be stored in a soft clean condition. After a final press operation, or after burnishing, ordinary brass products may be liable to season-cracking, and if so, and it is required that they should be quite free from this source of trouble, they should be finally annealed at a temperature in the neighbourhood of 250° C.

If failures occur during the working of brass, blame should not be immediately, laid upon its quality. The tool design, the annealing, and other details arising in the course of the manufacture should be reviewed, and not until these are found faultless should the blame be put upon the metal. The latter may, of course, be wrong; its manufacturer will be glad in his own interest to know of, and to give every help in eliminating defects ; but it should be remembered that the working of metals in power presses and by other mechanical means is in some instances in the hands of operatives who do not always visualise the properties-and changes in properties-that take place when a metal is being worked or annealed. Quite innocently they may have departed from the correct routine. But when all is said, the engineer and the metallurgist, the metal user and the metal manufacturer, sometimes disagree as to the causes of failure. With a fuller appreciation by each of the difficulties that beset the other, such diverse views will tend to disappear, good will result, and progress in knowledge and practice be made. (The Cold-Rolled Brass & Copper Association.)