ZOOLOGY AND BOTANY, MIOBOSCOPY, ETC. 313 



follows : — A strong solution of ammonia is diluted with 3-4 volumes 

 of water, and carmine added in excess. After filtering, the solution 

 is mixed with the gelatine, and then enough acetic acid added to 

 change the dark purple-red into blood-red. It is not necessary to 

 completely neutralize the ammonia. The dry emulsion requires only 

 to be placed in water for a few minutes and melted over the water- 

 bath to be ready for use. 



Blue Emulsion. — A slightly modified form of Thiersch's formula : — 

 1. To 300 ccm. of melted gelatine add 120 ccm. of a cold saturated 

 solution of green vitriol (ferro-sulphate). 



2. To 600 ccm. of melted gelatine add first 240 ccm. of a saturated 

 solution of oxalic acid, then 240 ccm. of a cold saturated solution of 

 red prussiate of potash (potassic ferricyanide). 



3. No. 1 poured slowly into No. 2 while stirring vigorously ; the 

 mixture heated for 15 minutes. 



4. After cooling, the emulsion is pressed through netting, the 

 vermicelli washed and spread on waxed paper for drying. In this 

 case the vermicelli must be dried directly, as they do not melt well 

 without the addition of oxalic acid. 



The dry vermicelli are prepared for use by first soaking in cold 

 water, and then heating with the addition of oxalic acid enough to 

 reduce them to a liquid. 



Black Emulsion. — 1. Soak 500 g. gelatine in two litres of water 

 in which 140 g. of common salt have previously been dissolved, and 

 melt the mass on the water-bath, 



2. Dissolve 300 g. nitrate of silver in one litre distilled water. 



3. No. 2 poured very slowly into No. 1 while stirring. An ex- 

 tremely fine-grained emulsion may be obtained by using 3-4 times as 

 much water in Nos. 1 and 2. 



4. No. 3 pressed into vermicelli as above, and then mixed with 

 No. 5. by clear daylight. 



5. Mix IJ litre cold-saturated potassic oxalate with 500 ccm. of a 

 cold-saturated solution of ferro-sulphate. 



6. No. 4 mixed with No. 5 gives a thoroughly black emulsion, 

 which should be washed several hours, again melted, and finally 

 poured in a thin layer on waxed paper. 



A grey-black emulsion may be obtained by using 240 g. potassic 

 bromide in the place of common salt in No. 1, the remaining opera- 

 tions being the same. 



Schering's Celloidin for Imbedding.* — Mr. G. C. Karop finds 

 that a form of pyroxylin, known as Schering's patent celloidin, used 

 by photographers for making a uniform quality of collodion, is an 

 excellent material for imbedding. It is in the form of flat cakes of 

 extremely tough, horny consistence, and " said to be non-explosive," 

 burning like paper, and simply carbonizing if heated in a test-tube. 



" A sufficient quantity is cut up and dissolved in equal parts of 

 absolute alcohol and absolute methylated ether 0-717, until the 

 solution is thin enough to pour. This takes some time, and the 



* Journ. Quek. Micr. Club, i. (1884) pp. 327-8. 

 Ser. 2.— Vol. IV. v 



