130 PREPARATION AND MOUNTING 



digest without heat from twenty-four to thirty-six hours, or until 

 the carmine is dissolved. Then take a Winchester quart bottle, 

 and with a diamond mark the spot to which sixteen ounces of 

 water extend. The coloured solution must be filtered into the 

 bottle, and to this pure water should be added until the whole 

 is equal to sixteen ounces. 



Dissolve 600 grains potash alum in ten fluid ounces of water, 

 and add to this, under constant boiling, a solution of carbonate of 

 soda until a slight permanent precipitate is produced. Filter and 

 add water up to sixteen ounces. Boil and add the solution to 

 the cold ammoniacal solution of carmine in the Winchester quart, 

 and shake vigorously for a few minutes. A drop of this placed 

 upon white filtering-paper should show no coloured ring. If much 

 colour is in solution the whole must be rejected, because, although 

 it is possible to precipitate all the colouring matter by the addi- 

 tion of ammonia or alum, it is not well to do so, as the physical 

 condition of the precipitate is thereby altered. 



Supposing the precipitation to be complete, or very nearly so, 

 shake vigorously for at least half an hour, and allow it to stand 

 until quite cold. The shaking must then be renewed for some 

 time, and the bottle filled up with pure water. 



After allowing the precipitate to settle a day, draw off the clear 

 supernatant fluid with a syphon. Repeat the washing until the 

 clear liquid gives little or no precipitate with chloride of barium. 

 So much water must be left with the colour at last that it shall 

 measure forty fluid ounces. 



For the injecting fluid take twenty-four ounces of the above 

 coloured liquid, and three ounces of good gelatine. Allow these to 

 remain together twelve hours, and then dissolve by the heat of a 

 water bath ; after which it should be strained through fine muslin. 



As this injecting fluid contains gelatine, the hot water, and 

 other contrivances mentioned in a former part of the chapter, 

 will be necessary here also, but no peculiar treatment will be 

 required. 



