STAINS AND STAINING. 285 



D. — Make a barely alkaline saturated solution of hrematoxylin 

 in water. For staining, place eight or ten drops of D in a watch- 

 glass half filled with C. 



The peculiarity of this modification is the presence of a quan- 

 tity of chloride of calcium in the solution. Its general use is for 

 staining in bulk, and the idea is that the presence of soluble salts 

 in the staining fluid will set up diffusion currents between it and 

 the fluids in the mass to be stained and so aid the penetration of 

 the stain. So far well, but when we come to add alum to the 

 solution we are at once met with double decomposition between 

 the alum and the calcium chloride, resulting in the precipitation 

 of sulphate of lime. 



The extent of this decomposition depends partly on time and 

 agitation, but principally on the condition of the alum. Here is a 

 bottle of the saturated chloride of calcium solution in which alum 

 crystals have been shaken at intervals during the whole of the day, 

 and the decomposition is visibly very slight. Here, on the other 

 hand, I have a quantity of the chloride of calcium solution, to 

 which I 2idi^ powdered 2\\s.xi\ instead of crystals, and shake. In a 

 few minutes it will be a solid mass. Which of these two modifi- 

 cations is intended by the inventor of the solution and the various 

 book-writers who have copied his formula ? 



It would appear from the Quarterly Journal of Microscopical 

 Science of 1879 ^^""^^ Kleinenberg himself used the following pro- 

 cess : — " Prepare a saturated solution of calcium chloride in 70 per 

 cent, alcohol, with the addition of a little alum ; after having fil- 

 tered mix I volume of this with 6 to 8 volumes of 70 per cent, 

 alcohol. At the time of using the liquid, add as many drops of a 

 concentrated solution of haematoxylin in absolute alcohol as are 

 sufficient to give the required colour to the preparation of greater 

 or less intensity according to desire." 



In this later form the saturation of the alcohol with alum is 

 omitted, but as alum is soluble in 70 per cent, alcohol, only about 

 I in 1000, this can make little or no difference. But as the addi- 

 tion of " a little alum " to an unknown quantity of saturated 

 solution is still far from definite, I have suggested the following 

 formula : — 



