Science & Invention,

Alexandra Herald and Central Otago Gazette, Issue 653, 9 December 1908, Page 7

Science & Invention,

CUTTING METALS WITH

OXYGEN.

A stream of oxygen is the wonderful "knile" now being used to cut metals. The operation is, performed by means of a blowpipe with two nozzles, of which the nrst delivers,an ignited j§t of mixed oxygen and hydrogen, and the- second a stream of pure oxygen. The pressure is tegulated by a gauge attached to the oxygen tank. The oxyhydrogen flame and the Stream of oxygen strike the same part of the metal, which, after being heated by the flame; is cvt> or rather burned, through by .the oxygen, the temperature being raised to' 1,300 or 1,400 deg. F. by the combustion of the metal. The "oxhydric'? cut is as smooth as a sheared cut and requires little or ho finishing. The chemical composition ,and physical properties of the material are not affected beyond a distance, of 1/100 inch from the cut. The: precision of the cut varies from 1/25 inch in plates less than 2 inches thick to 1/6: inch in the thickest objects, and the ividth of the cut varies from i to 1/5 of the thickness.

Armour plates can now be cut by this means in one-twentieth, of the time required for mechanical cutting, and the sharply localised heating probably causes less strain than punching and shearing develop; The cost of cutting by oxygen is actually only about half the cost of mechanical cutting. The advantages of the, process are well shown in our illustrations, and, the extraordinary possibilities of the system are illustrated by the following examples, taken from actual practice. In the dust catcher of a blast furnace, made of i-inch. plates, seven openings for branch pipes, each 8; feet in diameter, and four holes over 2 feet in diameter, were cut by two men in 6 hours at a total cost, for labour, gas, etc., of £3. • It would have taken two men at least two days to cut one ot the large holes with hammer and chisel. A sinkhead/ 3 inches thick and 16 inches long was removed from a steel casting in 4 minutes with under two shillings' worth of gas. A sinkhead li inches thick and* 10 inches long was cut from the flange of a valve case in 3 minutes.: Three runners about 2 inches thick and with .an ' aggregate length of 30 inches were cut neatly from the flanges of another valve case in 11 minutes at a, cost of two and fivepence. The removal of runners and sinkheads with planing and shaping machines is a very ' difficult, tedious, and expensive Operation; and after it is completed it is necessary to send the castings back from the machine shop to the foundary to be annealed, The oxhydric process is'applied in the foundry to castings hot from the mould, which are annealed before they go to the machine shop for finishing. The oxyhydrogen nozzle of the oxhydric apparatus is cooled by water and other heat absorbed so effectually, that flame striking back is immediately cooled below the point of ignition, and consequently extinguished, so that all danger of explosion is eliminated. The cooling device also serves the purpose of mixing the r> - ases intimately/

WHY WE SEE SPECTRES IN THE V DARK. Every one must at times have asked himself why familiar objects in a dim light tend to "assume fantastic and oftentimes alarming appearances. Who, m walking across the fields after sunset, has not at times been startled by some shadow of uncertain outline and disconcerting mobility that has fallen upon the retina ? It is not a question of courage because the boldest of men may experience a momentary feeling of apprehension and the reflex movements to which the impression; gives use are the outcome of the instinct of self-preservation which is notoriously most active in presence of a danger the nature and extent of which are for the time unknown. Habits of mental analysis and selfcontrol, of course,, mitigate the effects of the visual impression which attain their maximum in the young and the inexperienced, but the general effect is the same, and we all know what it is to check a sudden impulse to run away. The explanation, our contemporary consider!, is to be found in the special conditions of night vision. The pupils are widely dilated and, as in the photographic lens iwith a large diaphragm, the apparatus of accommodation can only focus for one plane. As the faculty of estimating distances is in" great measure lost in the obscurity we cannot focus with precision, and a blurred uncertain outline is thrown upon the retina. , Then, too, colours viewed iii a fading light lose their distinguishing hue in a fixed sequence until a point is reached at which everything' becomes of one uniform grey tint, whence nfl doubt the origin of the French pro verb, ''la nuit, tousles chats sont gris" (all cats aire grey in the dark). The impression of form is principally trarismtited by the retinal cones which are most abundant in the centre of the retina, whereas the appreciation of light and shade is provided byf,'the rods, so thai in man under the ence ; of >' dim; light, there is; far more rapid; depreciation of central than- of peripheral vision. -