PICRO-SULPHURIC ACID. 37 



(see PICRO-SULPHURIC ACID, PICRO-NITRIC ACID, PICRO-HYDRO- 

 CHLORIC ACID and the directions there given). 



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

 Sci., April, 1879, p. 208; MAYER, Jo urn. Roy. Mic. Soc. (N.S.), 

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

 fying 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 may also, in any 

 case in which confusion is likely to arise, b6 called "concen- 

 trated " 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 about 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 Arthropods. I may as well say at once 

 that in my opinion this practice should be reversed, for I 

 think it will be found 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 

 cold, with which weeks may be required to fully remove the 



