302 CHAPTER XXTI. 



486. Foi/s Carmine-Gelatin Mass (Zeit. f. wiss. ZooL, 

 xxxviii, p. 492). 



This can be kept in the dry state for an indefinite length 

 of time. (FoL finds that the addition of chloral hydrate to 

 wet masses is not an efficient preservative.) 



One kilog. of Simeon's photographic gelatin* is soaked 

 for a couple of hours, until thoroughly soft, in a small 

 quantity of water. The water is then poured off and the 

 gelatin melted over a water-bath, and one litre of concen- 

 trated solution of carmine in ammonia is poured in with con- 

 tinual stirring. (The carmine solution is prepared by diluting 

 strong solution of ammonia with three or four parts of water 

 and adding carmine to saturation ; the undissolved excess of 

 carmine is removed by filtration just before the solution is 

 added to the gelatin.) 



To the mixture of gelatin and carmine,, which should have 

 a strong smell of ammonia, sufficient acetic acid is added to 

 turn the dark purple colour of the mixture into the well- 

 known blood-red hue. Exact neutralisation is not necessary. 

 The mass is set aside until it has become firm, and is then 

 cut up into pieces, which are tied up in a piece of tulle or 

 fine netting. By means of energetic compression with the 

 hand under water (it must be acidulated water, O'l per cent, 

 acetic acid, otherwise the carmine will wash out ; cf. Journ. 

 Roy. Mic. Soc., iv, part 3, 1884, p. 474) the mass is driven 

 out through the meshes of the stuff in the shape of fine 

 strings, which are washed for several hours in a sieve placed 

 in running water in order to free them from any excess of 

 acid or ammonia. The strings are then again melted, and 

 the molten mass is poured on to large sheets of parchment 

 paper soaked with paraffin, and the sheets are hung up to 

 dry in an airy place. When dry the gelatin can easily 

 be separated from the sheets, and may be cut into long 

 strips with scissors and put away, protected from dust and 

 damp, until wanted for use. In order to get the imiss 

 ready for use, all that is necessary is to soak the strips for 

 a few minutes in water and melt them over a water-bath. 



The process may be simplified, without giving very greatly 

 inferior results, as follows (Lehrb., p. 13). Gelatin in sheets 

 is macerated for two days in the above-described carmine 

 * Doubtless any good photographic gelatin will do as well. 



