01 MICROSCOPIC OBJECTS. 179 



use those given in that work. For red, however, vermilion, 

 as above stated, may be used; but it must be carefully 

 examined by reflected light to see whether it be free from 

 all colourless crystals or not. It must first be worked in a 

 mortar, and then the whole thrown into a quantity of water 

 and stirred about ; after leaving it not longer than a quarter 

 of a minute, the larger portions will settle to the bottom, 

 and the liquid being poured off will contain the finer powder. 

 This may then be dried slowly, or added to the size whilst 

 wet in the manner before advised. 



13. Yellow injection. To prepare this, take 



Acetate (sugar) of lead 380 grains. 



Bichromate of potash 152 



Size 8 ounces. 



Dissolve the lead salt in the warm size, then add the bichro- 

 mate of potash finely powdered. 



Some of the chromic acid remains free, and is wasted in 

 this solution, so the following is given : 



Acetate of lead 190 grains. 



Chromate of potash (neutral) . . . 100 

 Size 4 ounces. 



The first of these has the deepest colour, and is the most 

 generally used. 



14. White injection. This is a carbonate of lead : 



Acetate of lead 190 grains. 



Carbonate of potash 83 



Size 4 ounces. 



Dissolve the acetate of lead in the warm size, and filter 

 through flannel ; dissolve the carbonate of potash in the 

 smallest quantity of water, and add to the size: 143 

 grains of carbonate of soda may be substituted for the car- 

 bonate of potash. 



N 2 



