This metal even if not pure, can easily be machined and worked up, provided that the correct grade of metal for the purpose be used, and also that the right shaped tools be used at the proper speed and with ample lubrication. In lathe work plenty of clearance should be given to the tools used, and ample lubrication, water is as good as most lubricants for this purpose. In press work the main thing to watch is lubrication, lard, oil or vaseline is found to be effective, no special difference is required in the tools from those used in pressing brass, but the annealing required is considerably less than for brass. In spinning aluminium no trouble should be found at a circumferential speed of about 3,000 feet per minute, always provided that the proper grade of metal be used. In polishing the very finest obtainable tripoli or rouge powder should be used to avoid the appearance of a scratched surface. To give a frosted appearance sand blasting is frequently resorted to, using fine sand, afterwards finishing by scratch brushing. Another method is to get the surface quite clean and dip it into a strong solution of caustic potash or caustic soda until the metal turns black. Take the metal out then, and dip into water to remove the caustic soda solution, then dip into a solution of 24 parts of nitric acid and 1 part of sulphuric acid. Remove and after well washing, dry thoroughly.

To burnish use a steel burnisher with vaseline as a lubricant. (See Vol. I, page 50).

Aluminium Solder

A solder that will join aluminium to either aluminium, duralumin, aluminium alloys, tin, copper, brass, zinc, German silver, and practically all non-ferrous metals and alloys, will probably be welcomed by many readers. It is used entirely without flux of any description, indeed, if any of the usual fluxes be used, failure to make a joint is absolutely certain. It is sold under the trade name of " Zippo," in sticks of two different hardnesses, i.e., " medium " for all general purposes, and " hard " for exceptional cases only. The method of using is the same for both, but more care is required in handling the " hard " variety, as its fusing point is much nearer to the fusing point of aluminium than the " medium."

Instructions For Use

The surfaces to be joined together must be first very thoroughly cleaned by scraping with a stiff wire brush, scraper, or file, and made free from dirt or grease, and then warmed up with a blow lamp (or clean and very hot soldering iron, tinned with Zippo). No flux is used with Zippo, but a rather higher temperature is required than for ordinary solder. Zippo will easily adhere to the aluminium if the surface is constantly scraped over with a small scraper as the Zippo is applied, and the scraping done with a gentle pressure. It is essential that the surfaces be maintained at a sufficient temperature to melt the Zippo on contact. As soon as it is firmly adhering to both surfaces the joint may be made. The joint should be allowed to cool in air, and should not be quenched in water. Holes may be filled up with it in a similar manner. Better than a soldering iron is a blow lamp with this material as the temperature can then be easily kept right, not too cold for the Zippo, and not too hot so as to damage the aluminium, and do not be tempted to try using any flux, or acid.

Aluminium Vessels, Cleaning

(a) ;Aluminium pots and pans can be cleaned by rubbing with lemon juice or a mixture of silver sand and lemon juice. Well wash and polish the pan afterwards. These goods should never be washed in soda water, as it causes them to lose their lustre.

(b) ;To clean inside of any pan, boil in it water with green stalks of rhubarb, empty and scrape out inside, and if any furr be left, then repeat the operation.

(c) ;If green rhubarb is not available for (b) try any other green fruit that is not wanted otherwise.

Aluminium Pistons

From a paper read by Prof. A. H. Gibson before the Institution of Mechanical Engineers, it was shown that cast iron pistons have a maximum temperature of about 440° C, whereas under the same conditions aluminium pistons would have a temperature of about not exceeding 250° C. Also the aluminium pistons would develop about 6% more power, and consume about 8% less petrol.