SCIENCE JOTTINGS.

New Zealand Mail, Issue 1424, 15 June 1899, Page 13

SCIENCE JOTTINGS.

WHAT IS LIQUID AIR? If the temperature of a quantity of air is reduced to about 3-15 degrees below zero on the ordinary Fahrenheit thermometer, it changes into a liquid very like water in appearance. If a vessel containing a quantity of this air is open to the atmosphere, it will boil and rapidly change into its normal gaseous state. If it is shut up in an air-tight metal vessel, it will change quickly into the gaseous state, but on account of the small volume occupied by the air in the liquid state, when it becomes gaseous it will exert a pressure, as long as it is kept in the vessel, of something like six tons per square inch. If, however, the change is made to take place in a more rapid manner, so that the air is almost instantaneously turned into gas, the pressure produced by it may be from twelve to fifteen times as much. That is to say, we may make of the air an explosive of far greater power than any at present in use.

In the use of an explosive such as gunpowder or dynamite, the substance is exploded so as to undergo this exceedingly rapid change from the solid to the gaseous state, and liquid air used for the same purposes should likewise be made to pass almost instantaneously from the liquid to the gaseous state. The reason why this power has not been made use of up to the present is, in the first place, that the cost of liquefying air is very great, a considerable plant of powerful machinery being wanted. But during the last three, years much has been done towards producing it more cheaply. Secondly, the great explosive power itself has been in the way. Liquid air, though handled with impunity by a man like Professor Dewar, produces terrible effects when incautiously exploded. It will probably be found when the full account of the experiments telegraphed above comes to hand that some substance such as cotton is used to mix with it, so as to produce a more manageable article, in the same way that gun-cotton and dynamite are manufactured.

The anoliealion of liquid air to firearms may still be looked on as doubtful, for the explosives actually used in firearms are by no means the most powerful known, as if the explosive is too powerful, if the gases are generated too rapidly, the pressure produced in the cannon may be so enormous as to shatter the cannon itself. HOW I INVENTED THE MACHINE GUN. (By Hiram Maxim, in the " People’s Friend. ’) Many years ago, while firing at a target with a military musket, I was much surprised at the force of the recoil. It appeared to me on that occasion that this waste of energy might be profitably employed in loading and nring the arm, but it was not until I went to Europe, and, finding myself in Paris, with insufficient work to keep me fully employed, that I actually took up the question of automatic guns. I first made a drawing which I afterwards took to London, and, having obtained and equipped a. small factory there, I commenceu experiments with a view of evolving a gun which would load and fire itself. There was not a particle of data to go by. No one before had ever spent a single cent in experimenting with automatic guns. I first thought of applying the recoil to working existing forms of mechanism, but found that impracticable. I then designed and constructed a totally new mechanism and a totally new system of feeding. In the spring of 1884 I constructed the first apparatus ever made in the world in which the recoil of one cartridge would load another cartridge into the barrel and fire it. This apparatus is now in the South Kensington Museum in London, and labelled : ” This apparatus loads and fires itself by force of its own recoil, and it is the first apparatus ever made in the world in which energy from the burning powder is employed for loading and firing the arm.”

When it was first reported in London that an American electrician had succeeded in making a gun which had loaded and fired itself, everyone was incredulous; they looked upon it as Yankee brag or boast. Many people came to my place and wished to see the gun with their own eyes. I had fitted up a place in the basement where a gun could be fired with loaded cartridges, and my visitors increased daily. Everybody from the Prince of Wales down came to see what was then considered a nine days’ wonder, and it required a very considerable portion of my time to receive visitors and show the arm; in fact, so much of my time was consumed that it became necessary to work nights in order to carry out the work and take out the patents in the various countries of the world.

I used fully 200,000 rounds of cartridges showing my first gun to visitors. The British Government was the first to give me an order. They asked me to make a gun which would not weigh more than 100 pounds, and which would fire 400 rounds in a minute. 1 presented a gun which weighed only 40 pounds and fired 2000 rounds in three minutes. At these trials I showed three different styles of automatic guns, and all were purchased by the Government, and are now in their museum.

The next step was to take the gun on the Continent, and put it in competition with guns working bv hand. Tn every case T was successful over all competitors, and received large orders. On returning to England T had a field trial before Lord Wolselev. Everyone admitted the superiority of the arm, both as regards accuracy, simplicity, and ease of manipulation, but His LordsMn said, on observing the enormous cloud of smoke given off by the gun, that the gun would be of little use in actual service unless it was provided with smokeless powder. ,4t that time there was no smokeless powder in England, althouah the French were conducting experiments with the view of finding a smokeless powder.

Acting on His Lordship’s suggestions, I then commenced making experiments with a view of making a suitable smokeless powder for my gun. The first powder which I made was pure tri-nitro cellulose, made from high-grade gun-cotton. This not proving altogether satisfactory, I added by degrees small quantities of nitro-gly-cerine, commencing with about 5 per cent., and increasing until I actually made a successful powder with as much as 60 per cent, of nitro-glyeerine; but, as there was great prejudice against the use of nitroglycerine, I reduced the quantity to about 13 per cent., and produced a thoroughly good smokeless powder. Both nitro-gly-cerine and high-grade gun-cotton are violent explosives. Sir Richard Webster, in the celebrated case of Nobel v. Government, admitted that I was the first man in the world to make smokeless powder with nitro-gly-cerine and gun-cotton. It was, I think, about nine years ago that I sent a quantity of this powder to this country. It was in competition with many other kinds of smokeless powder. It produced excellent results, and, according to the official report printed at the time, it was superior to any other powder submitted, and today it may be said that little or no improvement has been made in this original powder submitted by me at that time. The powder employed by the Government to-day is practically of the same composition, and the pressures and velocities are also practically the same.