PROJECTIONS. 31 



3. If india ink be rubbed up in water until it is quite 

 thick, it can be used for drawing designs upon ordinary 



glass. 



4. A thin sheet of gelatin may be treated like the 

 glass coated with the transparent varnish, and either 

 have the design scratched upon it, or drawn with ink. 

 It should be inclosed between two glasses for protection, 



5. Thin sheets of transparent mica will receive lines 

 drawn with india ink, or the figures may be scratched 

 upon them with the needle or awl. 



6. Designs may be nicely etched upon glass, by first 

 coating the glass with a thin, even coat of beeswax, 

 which can be well done by heating the glass over a 

 lamp until the wax melts and flows over its upper sur- 

 face. When it is cool, draw the design with a needle 

 point or a small awl, cutting through the wax all the 

 way. Take an old saucer, or some such dish which you 

 are willing to spoil for other use, and put into it a table 

 spoonfull of powdered fluor spar. Upon that pour a 

 table spoonful of strong sulphuric acid, and stir them 

 together with a stick. Fasten the glass, drawing upper- 

 most, to a piece of board large enough to completely 

 cover the dish. The fastening can be done by crowd- 

 ing tacks into the wood, so that the heads shall lap the 

 glass and keep it in its place. When thus fixed and 

 laid over the mixture of spar and acid, gently heat the 

 dish, being careful not to inhale the fumes that will 

 escape. When the fumes begin to appear, put the 

 whole either out of doors or in a good chimney draught, 

 and let it remain eight or ten minutes, when the wax 

 may be removed by heat and rubbing, and the drawing 

 will be found etched into the glass. 



Beautiful pictures of crystals can be made in this 

 way, by taking various crystallizable salts, such as am- 



