In the nineteenth century oxy-hydrogen limelights were used extensively for theatre spot-lights and in magic lanterns. When an oxy-hydrogen flame was directed onto the surface of a block of lime, the lime gave off an intense white light, which could be focussed on hand-painted or photographically prepared slides in a magic lantern, which were then projected on a white calico screen.
The limelight was used to provide a brilliant white light for the projection of slides in the magic lantern (q.v.) during the 1800s and early 1900s. Oxygen was burnt with hydrogen, ether, acetylene or coal gas and the flame directed on to the surface a cylinder or ball of lime. The intense heat of the flame produced a small spot of white-hot lime which which became the source of an intense white light that was focussed onto the lantern slide by condenser lenses.
There were three variations of the limelight. The oxy-calcium lamp, the oxy-calcium jet and the oxy-hydrogen jet. In all three types a flame was directed on to a block of lime but the method of combustion varied and the intensity of light was not the same.
The oxy-calcium lamp used a jet of oxygen blown through the large, loose flame of a spirit lamp to heat the surface of the lime block, but the light was not very strong. The oxy-calcium jet was similar, the oxygen being directed through the flame of a second jet burning hydrogen or coalgas and gave a better light than the oxy-calcium lamp. These lights were used in small halls and were ideally suited for travelling shows as only one gas bag was needed, for oxygen.
The most intense light, however, was produced by the oxy-hydrogen jet, where the oxygen and hydrogen were mixed together before being burnt. This flame was so hot it could burn a cavity in the lime and great care and constant adjustment was needed to produce a steady light. A mechanical arrangement let the operator rotate and raise or lower the lime cylinder so that a fresh part of the surface could be presented to the fiercely burning flame, and another adjustment altered the distance between the nozzle of the jet and the surface of the block.
Oxygen was generated by heating potassium chlorate in an iron retort. After being cleaned by bubbling it through water the gas was stored in a gasbag (see GASBAG below). A Sears Roebuck catalogue issued between 1905 and 1910 contains an illustration of an oxygen-making machine in which a compound called Oxylithe was mixed with water to provide a supply of oxygen.
|Left: A simple sketch showing how oxygen was made. Potassium chlorate was heated in a retort with manganese dioxide as a catalyst and the gas bubbled through a purifier which was usually a bottle containing water. The oxygen was then piped to a gas bag for storage.|
Due to inexperience and impure chemicals many attempts at making oxygen ended in failure and, much worse, disastrous explosions. Two such explosions occurred in Adelaide.
In July 1866 the Register drew attention to the risks involved when attempting to produce oxygen. The newspaper reminded the public of an explosion that had occurred under George Freeman's studio in 1864. Three photographic artists, Messrs. Freeman, Cornock, and Stone, were engaged in making oxygen on Mr Freemans premises in Hindley street, when a loud report was heard, a cry of fire was raised, the fire-bell was rung, the engines brought to the spot, and a general alarm was raised in the city. On investigating the cause of the explosion, it was found that the gentlemen named had placed upon the fire a retort filled with gas-making materials. The retort was scarcely heated, when it exploded with a loud report. The room with its furnishings was almost entirely destroyed; Mr Freeman was seriously injured, and lost the sight of an eye; and Mr Cornock subsequently experienced a long illness, brought on by inhaling the suffocating gases which the explosion produced. The manganese in this case had been procured from a respectable chemist in Adelaide.
Now, said the Register, there had been another explosion.A week or two ago [June 1866] Mr Cornock, a little daunted, but not intimidated by his previous experience, procured from the same chemist a second supply of manganese, with the usual proportion of chlorate of potash. Having been duly assured of the purity of the materials he commenced, in conjunction with Mr Dobbie (q.v.) of Gawler Place, a second gas-making experiment. As in the previous case great care was taken in the adjustment of the apparatus, but the fre had scarcely obtained access to the retort when the whole thing again violently exploded, nearly destroying the premises, the operators having a narrow escape with their lives.
Gasbags were used to store the gases required to produce the flame used in the limelight. Two bags were needed, one for oxygen and another for the fuel, which was normally hydrogen, although coal gas could be used. The bags were made of two layers of stout twill cloth with a layer of rubber in between, and a later improved method used vulcanised rubber membranes.
The gas was pressurised by trapping the bags between boards held together by a wedge frame, the top board being held down by very heavy weights, 56 pounds (25 kg) for an 8 cubic foot single bag used for the oxy-calcium light. At least three times that weight (75 kg ) was needed for a double bag used to supply oxygen and hydrogen for the limelight proper. In 1890 gasbags with a capacity ranging from 3 to 12 cubic feet were available with skeleton pressure boards, and when deflated they occupied very little space. Gas compressed at high pressure into iron cylinders fitted with regulators eventually replaced the gasbags.
|Below left: A
pair of gas bags used to supply oxygen and hydrogen to a limelight.
Below right - A single gas bag showing where the weights were placed to apply pressure to the gas. Used to supply oxygen for the oxy-calcium lights.