APPARATUS FOR KEEPING TEMPERATURE CONSTANT.
Another method of keeping constant the temperature of solutions is by means tube with tap, such as is used in a burette. This, however, is not absolutely necessary. The arrangement will answer very well without it, but if one is at hand by all means use it, for it is a con venience. If desired, a rim of tin may be placed over the top to cover in the hot water. The water jacket is now ready. If a Bunsen or a small lamp flame is available to place beneath the jacket, all that is necessary is to fit the funnel through the opening in the cork, and through the cap or sheet of metal, filling it nearly with cold water through the opening at the top by means of a second funnel. When the water is suffi ciently warm, the filtering medium and the of the apparatus shown in Fig. 137. This consists of a glass funnel around which is coiled india-rubber tubing, fas tened by means of thin wire, so that one end may be attached to the hot water supply, while the other, allowed to remain free, runs off into the sink. An efficient
and permanent heating arrangement may be made by coiling compo pipe around a tin plate funnel and using an inner glass funnel for filtering. Steam or hot water is passed through the coil of pipe. The ap paratus might be made with glass tubing, if preferred, by anyone accustomed to bending this. A block of the same shape would be necessary, around which the ' tubing could be allowed to fall as it warmed. There are several operations in photography where this method might be useful. The next consideration is the filtering medium ; some workers recom mending one, and some another. For this purpose, washed wool and chamois leather are equally good. It is essential that filtration should be thorough, and although the emulsion may be made to run more quickly through wool, it is possible the operation may have to be repeated, so that there is no advantage in the end. A good practice is to use swansdown