AND HOW TO USE IT. 47 



neutralised. Now mix the two solutions at a temperature of 

 40*^ C. (104 F.) 



Dr. G. Sims Woodhead's Mass.— Take of carmine (pure) 

 4 parts, by weight ; Uq. ammonia, 8 parts, by measure ; gelatine 

 (Cox and Coignet's), 10 parts, by weight ; distilled water, 100 parts, 

 by measure. Put the carmine in a mortar, and pour on the 

 ammonia, when an almost black paste will be formed, if the 

 carmine is pure ; pour on the water, and set the solution aside to 

 filter. Place the gelatine in a narrow glass jar, and add sufficient 

 distilled water to cover it, and allow it to stand until the gelatine 

 is thoroughly softened. Warm the carmine solution in a pan of 

 water (kept nearly boiling on a gas jet, or near the fire), and add 

 the gelatine ; stir thoroughly, and add a 10 per cent, solution of 

 acetic acid, drop by drop, until the alkalinity of the ammonia is 

 neutraUsed, and the fluid even slightly acid. The point at which 

 this takes place will be recognised by the pungent odour of the 

 ammonia becoming gradually lost, and that of the acid substi- 

 tuted, and the fluid loses its bright carmine, transparent colour, 

 and turns a dull brownish red. With the exception of the change 

 of colour test, I prefer Stirling's method, which, however, is greatly 

 improved by making a diluted acetic acid solution, by adding the 

 acid to I or 2 drachms of water, when the pouring to or adding 

 is more easily controlled. It will be noticed that Dr. Woodhead 

 takes a I o per cent, solution. 



Blue Mass.— This is made by adding soluble Prussian blue in 

 place of the carmine. Take of soluble Prussian blue 4 drachms ; 

 gelatine, 4 ounces ; distilled water, 2 ounces. Treat the gelatine 

 the same as in making the carmine mass, using half the water ; 

 then add the Prussian blue dissolved in the other half of the 

 water, keeping both solutions hot, and constantly stirring whilst 

 cooling is going on. 



Thiersch's Transparent Yellow- — Requires a considerable 

 amount of care to be exercised in its preparation. It is made as 

 follows :— Take of (a) chromate of potash i part, water 1 1 parts, 

 dissolve, (if) Nitrate of lead i part, water 1 1 parts, dissolve. Mix 

 I part of a with 4 parts of a concentrated solution of gelatine 

 (made by washing good gelatine for an hour in distilled water, and 



