Science.

Alexandra Herald and Central Otago Gazette, Issue 369, 4 June 1903, Page 2

Science.

SAVING'S|E?»&TH. \ of the §[*W power is to. rest' l ;«st beford ge# v%9JFd tiag tired. A human being, says* •Health/"may work up to the point of fatigue without but the moment exhaustion supervene£,S„that moment a debilitated state sets in which cannot be from readily. To rest just Before getting tired will prevent breaking down, when, if mental or physical strain is continued, a? little too fan, recuperation may become difficult, j V\ ~**ZHE LIABIinTXJm^DJ^EKBaSU,^

People who are fond of statistics will be interested in tbe following details relating to deafness, collected by a French surgeon, Itappeafrf'thalrmen aural diseases than women, and that out of every deven middle-aged persona Jihere are two who do not hear so well with one ear as with the other. In every thousand children under fifteen years of age, four show symptoms of some ear disease,' and six a marked deficiency in hearing power The liability to disease increases from birth to the age of forty, and then begins gradually to decrease aa old age advances. Ont of the total number of cases sub'-' jected to surgical treatment, it is estimated that about 63 per cent, are cured, and 30 per cent, permanently relieved.

THE NEW BBICKLAYING: MACHINE. Our friends in the bricklaying trade will have to quicken their pace, or they will find themselves superseded altogether now .that bricklaying by machinery has become possible. According to a Consular report, a recently invented Canadian machine, worked by two men and a lad, will lay 400 to 600 bricks per?hour. Door and window spaces cause only a slight delay. The machine is suited for all plain work, such as walls, sheds, mills, factories, rows of cottages, piers of bridges, .etc. .Considerable pressure is put on the bndVs; and it is claimed} that* *he work id more -firmly done thanby, 'band.' '■' The invention will do the work of six or seven skilled bricklayers, and it is belived that a machine adapted to build a factory covering about 60ft. by 40ft. could he put on the market for .£IOO. The apparatus can be readily worked after a fortnight's instruction. r v \ .j

TO SOLDEE TIN W ABE. First clean all the parts to be soldered or the space round the holes to'be stopped. It is important that wherever the solder is to touch must not only be made" perfectly clean but be scraped bright, or the metal. will not slicks The\oopper bit or soldering-iron must also be made perfectly clean, each time;, you set about soldering, or it will neither tin itself nor help you to tin the goods. To prepare; the soldering-iron heat the copper bit till it is red-hot, then, witkan ; old : file, file i* perfectly clean on.all the faces. If you are. working at a proper brisk rate, by the time you.have filed it on all sides it will $6 the proper, heat for Ham ready a piece of sal ammoniae, and a piece of fine solder; burn a hole .with your bit in the top of your sal ammoniac, .and melt a little solder in it. Twist the bit about in the melted solder, and. you will find it will tin nicely. Now heat the bit, and -be careful (now the bit is tinned) not to let it net hotter than just on the cold side of red-hot, When taken from the fire dust the ends of the bit with a-piece of old" woolen cloth and give it a turn in the sal ammoniac, and if the tin is not burned off it will be as bright as silver, and work splendidly. All <his will perfectly. simple when practised a little. The best flux for tin goods is powdered resin; But many kitchen utensils that are called tin are, as a matter of fact 8 iron, tinned Over, consequently the more you oieaa them'the' more the iron comes to the, front. When cleaning these so-called tinned goods to be?ih your work, if you find a black patch shows, you may be sure that it is iron. You must file it clean,. but the flux you must use for this is what is known as killed spirits of salts. To make this you have only to* put some spirits of salts in an earthenware crock, and into the spirits put some clean zinc, cut in shavings, till it will disEolve no more. This flux will tin almost, anything except zinc, for which use spirits of-salts thinned, with a. little water J but .in;every case all the parts must be perfectly clean.

ETCHING, ON GLASS. VGlaßSvis'.efcHed|By hydrofluoric acid or hydrofluoric acid gas. Tha gaseous acid has the property of producing a surface which resembles ground glass in its appearance; the'liquid'aci'd produces clear etching. Etching 'glass, therefore, con-?,-sists of two distinct branches, Ist, =s&<&; production of - a dull I image on a 4ea% surface (when the gas is used); 2nd, the• production of a clear image on a surface. previously ground or dulled by means of the liquid acid. Ist, the' glass plate to be etched is cleaned and ;gently warmed until hot enough to melt .wax. The surface is then covered with aa equable layer of white wax by rubbing the wax over it. When cold, the design is eufc out of the wax with a graver. A shallow leaden trough-, about the size of the plate (but a trifle smaller) is obtained,.,into which is placed a small quantity of finely-powdered fluorspar. This must be weighed and then gently sifted over the bottom of the trough. To every two parts by weight of . fluorspar add three of good oil of vitriol. Stir quickly with a wooden stick, and place on the hob or other warm place. Vapourwjll booh rise.? Now remove the trough and cover over with the waxed and graved plate, waxed side downwards. In a very short time the acid wilt have etched the bare portions of' the glass.. jWhen sufficiently etched, remove the wax by melting. Conduct these operations under a chimney, to carry off the vapours, as they are very injurious. To prepare the acid for clear etching, place two parts J fluorspar; and three v& sulphuric acid in a leaden retbrtj 'the Mbe of which must dip into a leaden bottle half-filled with water. Apply; heat to the. retort as long as'-the; absorb the fumeß generated. If a ground glass be prepared with wax, as above, and a ledge of wax or putty Jje.made round it, on pouring itib -liquidacic| on the plate, clear lines <i)a tie dullj {ground will result, or a 'flashed coloured glass may, by the same be made to present a colourless; .picture on a coloured ground.. The sheets, of clear glass' may themselves be dulled by "exposing them," without jpreviously waxing, to the fumes of the'acid gas. N.B.—Hydrofluoric produces most- painful and malignant ulcers.