OF MICROSCOPIC OBJECTS. 119 



Acetate (sugar) of lead ; 380 grains. 



Bichromate of potash 152 " 



Size 8 ounces. 



Dissolve the lead salt in the warm size, then add the bichromate 

 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 carbonate of potash. 



15. For blue injection, which is not, however, much used with 

 reflected light, as before stated, take 



Prussian blue 73 grains. 



Oxalic acid 73 " 



Size 4 ounces. 



The oxalic acid is first finely powdered in a mortar, the Prussian 

 blue and a little water added, and the whole then thoroughly 

 mixed with the size. 



16. It may here be repeated, that it is only when the capillaries 

 are to be filled that there is any need to be at the trouble to pre- 

 pare the colours by this double composition ; and, indeed, colours 

 ground so finely may be procured that the above instructions 



