For any ordinary lantern entertainment, providing the worker has an efficient jet, a 6-ft. gas bottle, which only measures 14 in. by 4 in. and weighs 10 lbs., will be found sufficient ; but most workers will prefer for home use a bottle holding 12 or 15 ft. of gas, which keeps indefinitely and may be used as required. To deliver the gas from the bottles to the jet, either a fine adjustment valve or a regulator is essential, the latter being the better arrangement. If the regulator is attached to a pressure gauge the exact amount of gas in the cylinder can be noted. Where coal-gas is laid on to the house, only one bottle is required, but, where there is no gas, it is necessary to have a second bottle of hydrogen or coal-gas, or else a " Saturator."
One of the best Saiturators is that known as the "Pendant," and this consists of a metallic box filled with absorbent material saturated with methylated ether, through which oxygen is passed, and this enriched oxygen is supplied to the hydrogen side of a mixed gas burner, while the oxygen tap is connected direct to the oxygen cylinder as usual. The manipulation is then exactly the same as described when using the two gases. It is a little remarkable that Saturators are not used to a greater extent than they are, for instruments of the Pendant type are safe and very easy to manipulate. Moreover, they are much smaller and more convenient in every way than a gas bottle. The No. 1 size measures 13X7X4, weighs about 7 lbs. and is sufficient for jets not consuming more than 3 1/2 feet of oxygen an hour, while the No. 2 of the same size and weighing 8 lbs. is suitable for jets of any power. The only adjunct necessary, apart from a cylinder of oxygen, is some good quality methylated ether •717 sp. gr., although gasoline of •650 s.g. may be substituted if the apparatus and oxygen are warmed.
Of course, there are some places where cylinders of gas are out of the question, and the modern way to make oxygen for medical or scientific purposes is by means of an " Oxygenerator." This apparatus is constructed to hold a chemical compound known as " Oxylithe," and this gives up oxygen on the application of water, much as does the acetylene generator produce acetylene gas.
There is, however no smell and oxygen not being explosive when mixed with air the process is absolutely free from danger. Moreover, the oxygen produced in this way is chemically pure, and such as is not readily obtainable by any other process. The "Oxygenerator " is of strong construction and takes to pieces when not in use. It weighs 25 lbs. and holds 24 cubes of " Oxylithe " (2 1/4 lbs.), which produce 7 cubic feet of the gas at a pressure of 2 lbs. to the square inch. The " Oxylithe " is sold in hermetically sealed tins and costs 2/6 per lb. The great advantage of such a piece of apparatus for home use is due to the fact that any small quantity of gas can be made at a moment's notice, and gas of such a quality that it may be used for medical purposes should necessity arise.
The Pendant Saturator.
The " Oxygenerator."
THE ARC LAMP.
The electric arc lamp for lantern use has undergone many improvements, and excellent automatic arc lamps, which obviate the hand adjustments of the carbons, are now procurable. Generally speaking, arc lamps are better when used with " direct " or continuous current, because with this current a crater is formed in one of the carbons, giving an intense spot of light. With the alternating current the light is shed in all directions, and the loss that occurs is minimised by setting the carbons at an angle to each other, so that the two terminals are pointing towards the condenser. There is also the drawback of a continuous humming noise when the alternating current is used. Then the voltage or pressure of the current is important. If the voltage is high there is necessarily a great waste of current, which has to be absorbed by a resistance frame,converting the surplus into heat. Most arc lamps require about 60 volts, the resistance which the air separation makes to the passage of the current between the two carbons, but, in practical use, a resistance frame is necessary, because without it when " striking the arc," or in other words, bringing the points of the two carbons in contact to start the current through the apparatus, we remove the air resistance for a moment, and were we not provided with such a resistance frame to convert the excess of supply into heat, we should melt our " fuses," or burn up our apparatus. It is, therefore, preferable to use arc lamps on a " direct " current at a voltage of 100, the extra 40 being absorbed in a resistance frame which acts much as a governor and steadies the light.