In many operations where glass vessels are used, success will depend upon having the glass perfectly clean. Upon this subject a correspondent of the Chemical News says: Such a subject may seem too simple, but yet the more I see students at their work, the more I am impressed with the fact that but few know how to wash a beaker-glass clean. Some time since I took beakers from various students in my laboratory (which they had washed and put away), and held them under a powerful stream of water until they were thoroughly wet. On taking them from under the spout, in almost every case the water ran off the glass in spots, showing that the glass was greasy. The best thing to wash beakers, etc., with, according to my experience, is sand-soap. Naturally, the sand must not be sharp. The soaps containing infusorial earth are most excellent for this purpose. Borax soap is also very efficacious. A piece of board about 20 cm. long, 15 cm. wide, and 4 cm. thick, should be screwed on to the right (inside) of the sink. In this block a rectangular hole, about 2 cm. deep and 1 cm. smaller than the section of the soap when stood on its long end, is to be cut. The bottom of the cake of soap is then whittled away so that it fits tightly in the hole. It is now moistened and pushed into the aperture, where it remains tightly fixed. By wetting the right hand thoroughly, and rubbing on this soap ridge, a good lather is made. With the soapy hand the glass is rubbed and washed until, on taking it from under the stream, no oily spots appear, the glass appearing wet all over. The beaker is then dried with a good towel (" glass towel "), and finally polished with a piece of chamois or kid leather. The final polish with kid is necessary, since the best towel leaves fibres on the glass. In cleaning test tubes, it is only necessary to rub the probang on the soap.
For cleaning flasks and bottles which have been soiled with varnishes or resins, or for cleaning the glass slides used for microscopic objects, proceed as follows: Remove all the balsam, resin, varnish, etc., possible by means of heat, scraping, and a solution of soda or potash. When the article is as clean as possible, place it in strong sulphuric acid, to which must be added as much powdered bichromate of potassa.
The chromic acid will quickly destroy all organic matter, and the article when washed in pure water will be found perfectly clean.