1929-09-21 — Page 13

THE HONGKONG TELEGRAPH. MOTORING SUPPLEMENT.

WHAT HAPPENS INSIDE.

Photographing Explosions.

The revolution in world trans exactly happens inside the cylinder port brought about by the patrol of a car engine when the spark engine has created an immense Ignites the mixture of petrol Interest in the cause and results of vapour and air? Most people pro- the explosion of gases. What bably have the idea that such an

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explosion is instantaneous, and though, broadly speaking, this is true, they do hot realize that

HUGE JUNKYARD.

actually the mixture is burned at Makes Streets Safer.

a high rata of speed.

Photographs of explosion flames travelling at over 21,000 miles an hour can now be taken, giving an accurate pictorial record of each phase of the explosion. This is achieved by the use of a camera behind the open shutter of which a strip of film is carried on a drum of dualumin alloy, rotating at a maximum speed of 18,000 revolu- tions per minute. Two hundred yards of negative are flashed past the lens in each second,

|

PAYING BUSINESS.

St. Louis, USA, Aug. 12th-~~- With one huge automobile "grave yard," the St. Louls Automobile Dealers Association is removing 12,000 potential accidents in the ["form of unfit automobiles from the road every year and making money from a resulting junk business.

Through a central organization, the autos are purchased from deal- ers who have taken in decrepit cars as part payment on new ones, and through a systematic junking and scrapping stockholders are realiz ing a tidy proat.

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Erraneous Theories. When I first commenced to in- vestigate the phenomena of ex- plosive gases, I was driven to the conclusion that existing theories regarding their nature were erron-

Many of these cars are towed eous, writes Reginald Fraser in into the junk yard. Some are "The Motor." Explosions had been more than ten years old. All are produced scores of times under apdangerous to drive, and for this parently the same laboratory conreason the St. Louis Safety Council ditions and the results appeared locks on this organization as a more or less constant. I believed, means of preventing accidents. however, that these "constancies" were really coincidences, and after many months of research succeed- ed in proving my contention, In every experiment the same out- ward conditions had been con- stant: the shape of the vessel con- taining the gas was identical, the gas was ignited in the same manner, and initial conditions of pressure and temperature did not

vary.

The first step in junking the cars is to remove the tyres, batteries. and lamps. These are sorted for resale, if their condition warrants such.

The body then is removed from the chassis, the chassis dissembled

its condition does not warrant resale, and the trimming and other fixtures removed.

Parts of the body, if in good con- | dition, are sorted carefully and set up for resale. Axles, good fenders, rear end assembles, generators and miscellaneous parts of the motor and body can be bought there for nearly any type of car, providing it is an old model.

Parts of the body that are unfit for the market are cut into pieces and sold as old metal. ·...

Everything coming out of the car in the dissembly is carefully saved for utilization in some form, The hair and cotton in the sente are stored away. The leather is ground into & powder which is used as a fertilizer. The only the seat thing not used are springs, which are too light and unhandy to be packed and sold. These are junked.

But soon it was obvious that re- sulta were being varied by inward conditions over which the experi- menter had little control. These were the changing temperature, the immediate change in va! ime of the gas after ignition, causing turbulence effects, and sudden al terations in the chemical reactions involved in the burning of the burning of the gas, itself.

For

experimental purposes carbon monoxide was first explod- ed in a horizontal glass tube. This is one of the slowest gases in explosion, its possible rate of flame propagation being from to 2,000 metres per second. When ignited electrically, the flame passed Instantly before the lens of the camera, while the speed of the "film behind the lens was synchronized to that of the gas.

In the explosion of some gases the flame is quite invisible to the human eye, though, contrary to what one might expect, such gases do not possess the fastest flame rates. A slowly burning gas may often be invisible, whereas if that Commercial Explosives. speed were doubled it would emit Although to most people experi- quite a brilliant light. For in mental research in explosives in- visible explosions we employ ultra-stantly calls to mind the horrors violet rays which are generated, of war, it would be true to assert from high-voltage condenser that the commercial application of spark. These are then reflected explosives has acheved far more from a large concave mirror, and in the service of humanity than it thus in some cases the shadow of has ever done against it. Without an explosion travelling at an intimate, knowledge of the perhaps 650 m.p.h., and quite in action of solid explosives, bridge visible to the naked eye, is record-building, quarrying and even coal. ed on the film rotating at ap- mining could only be carried out proximately the same speed. Each at vastly increased cost. A mere photograph is in the nature of an two pounds of nitroglycerine can instantaneous snapshot and is as

do effectively in a few seconds separate and distinct.as in a

what would need the labour of a cinema film,

hundred men for many days.

Stupendous Flame Rates.

The slowest flame rate, observ ed in gaseous explosions is a mare 30 centimetres per second, while the highest is over 3,000 metres per second. In the case of solid explosives the flame rate increases rapidly, and with nitro glycerine will even reach 10,000 metres per second a speed of over 22,000 miles an hour!

Often the glass tube in which the explosion occurs is instantly shattered to fragments!

The problem that beset our early work was to obtain a good pictorial record of flames travelling at the almost inconceivable rate of two

spark. After that speed the eye is deceived into imagining the light to be continuous, for at full power 800 such flashes are reflect- ed each second from the concave mirror. Each flash occupies, a space of time equal to about 1/1- 000,000th of a second!

Experiments in this particular line will be carried out in the near future, when it is hoped to gain. fuller information as to the im- mediate results of the explosions of nitro-glycerine and dynamite. This field work will necessitate in some cases building shelter walls behind which the operator and his camera can work in safety. Less than 10 ft. distant, sufficient explosive to uproot a 10-roomed. house will be exploded in a hollow,' open-ended cylinder, and the data gained should be, of ramense value.

Further experiments will also be carried out Involving the ex- plosion of a quantity of nitro glycerine in a totally enclosed miles a second. Moreover, the old steel cylinder, in which is inset a adage, that the "enmera cannot small steel container of great lic," does not always hold good. strength. Behind this again will Everything recorded by the be built a brick wall, backed by a camera in such experiments must sheet of glass, while the camera be proved by ascertaining the will record a picture of the ex- history of the photograph. In plosion through slits measuring spite of all dificulties, however, no more than 1/1,000th of an inch a now camera costing £500 was in width. gradually evolved and perfected which, in spite of weighing 20 cwt., can now cope with the fastest flame rates we have yet been able to discover.

It is even possible to imprison gaa in the thinnest of celluloid, such as that used for covering so many chocolate boxes. That frail container is shattered in possibly 1/1,000th of a second, but the photograph is taken before the splinters of glass of celluloid even have time to move!

One of the simplest of hydrocar bon gases is methane, or firedamp Here the camera recorda a fast flame rate of 2,500 metres per second, since this gas, is more cx- plosive than carbon monoxide and possesses a much more complex combustion. So we rise in the speed scale until we get to a mixture of acetylene and oxygen, the explosion flames of which travel at 3,500 metres per second the fastest speed for any gas.

One of the interesting points about the condensér.spark giving out the ultraviolet rays for this highspeed photography is the in ability of the human eye to record à speed impression. When the number of sparks la cut down to a mere 15 a minute, the observer fa conscious that the light fa emanating from an Intermittent"

W16

Yet, in spite of all research, we. are still only at the threshold of knowledge in this department. How far we are from finality show, by the recent upheaval of gas mains in Hoborn and else where in London, the cause of which is still a matter for debate. Then there are those explosions in four mills, where grinding ma- chinery throws off into the air an immense number of minuto parti- clas of flour dust; It is also a little known fact that the coal dust present in the air of our mines is responsible for far more datal explosions than the dreaded 'fire- damp. Out of 100 or oven 600 experiments in the laboratory the scientist can often deduce only one certain fact. Yet he is to that extent nearer to success, and it should only be a question of time before, step by step, those frag ments of knowledge are chained to complete a whole.

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