PIORO-SULPHUEIC ACID. 39 



with sulphuric acid ; or with nitric acid, or hydrochloric acid, as suggested 

 by P. Mayer (see below). 



57. Picro-sulphuric Acid (KLEINENBERG, Quart. Journ. Mic. 

 Sci., April, 1879, p. 208; MAYBE, Journ. Roy. Mic. Soc. (N.S.), 

 ii (1882), p. 867). By picro-sulphuric acid, without any 

 qualifying term, I understand a fluid made (following Mayer, 

 1. c.) as follows : Distilled water, 100 vols. ; sulphuric acid, 

 2 vols. ; picric acid, as much as will dissolve (this will be about 

 0'25 vol. ; as the picric acid is much less soluble in sulphuric 

 acid solution than in water). This may also, in any case in 

 which confusion is likely to arise, be called " concentrated " 

 or " undiluted picro-sulphuric acid." 



By " liquid of Kleinenberg " I understand a mixture sug- 

 gested by Kleinenberg (1. c.), and best made by diluting the 

 concentrated picro-sulphuric acid prepared as above with three 

 times its volume of water. 



(Kleinenberg also directed the addition of as much creosote as would mix. 

 This was done with the idea of eliminating the swellings produced in some 

 objects by the liquid, but it has been found not to have the effect attributed 

 to it, and has been abandoned. FOL (Lehrb., p. 100) states that the same 

 end may be attained by adding one third vol. of 1 per cent, chromic acid.) 



Of these two formulae the one commonly employed is that 

 given by Kleinenberg the dilute mixture ; undiluted picro- 

 sulphuric acid being reserved for objects requiring special 

 treatment, chiefly Anthropods. I may as well say at once 

 that in my opinion this practice is erroneous, for I hold that 

 Kleinenberg's solution is much weaker than is desirable in the 

 majority of cases, and should be reserved for special cases, 

 such perhaps as that for which it was originally proposed, the 

 embryology of the earthworm ; and the concentrated solution 

 should be the one taken for general work. This particularly 

 applies to marine organisms. 



The treatment is the same in either case. " The object to 

 be preserved should remain in the liquid for three, four, or 

 more hours; then it should be transferred, in order to harden 

 it and remove the acid, into 70 per cent, alcohol, where it is 

 to remain five or six hours. From this it is to be removed 

 into 90 per cent, alcohol, which is to be changed until the 

 yellow tint has either disappeared or greatly diminished.'' 



Warm alcohol extracts the acid much more quickly than 



