I.MI5KDDING METHODS. 9 ( J 



these are seldom realised in the British Isles, and, whilst I 

 quite admit that such hard paraffin may have its raison 

 d'etre for Naples, I hold that for that very reason it is 

 in general unnecessarily hard for cooler climates. 



My recommendation of a relatively soft paraffin refers to 

 work with the Thoma sliding microtome. Microtomes with 

 fixed knives, such as the Cambridge, the Minot, or the 

 Reinhold-Giltay, will give good results with much harder 

 paraffin, and, in fact, require such. 



Stout knives of hard steel will take a harder paraffin than 

 thin ones of soft steel ; but the latter may be preferable for 

 soft masses. 



For thin sections a harder paraffin is required than for 

 thick ones. 



Hard objects require a harder paraffin than soft ones. 



BKASS (Zeit. wiss. Mik., ii, 1885, p. 300) recommends 

 paraffin that has been kept for some years, as it has 

 less tendency to crystallise than new paraffin. 



Paraffin of various melting-points is easily found in com- 

 merce. Intermediate sorts may be made by mixing hard 

 and soft paraffin. I find that two parts of paraffin melting 

 at 50 with one of paraffin melting at 36 C. give a mass 

 melting at 48 C., and a mixture of one part of that melting 

 at 53 with one part of that melting at 45 gives a mass 

 melting at 50 C. 



According to E. BUECHARDT (Jena Ztii. Naturw., xxxiv, 

 1900, p. 719) mixtures of paraffins of different melting-points 

 give better results than an unmixed paraffin of the same 

 melting-point as the mixture. He recommends 10 parts of 

 40 paraffin + 1 of 45 + 1 of 52 + 1 of 58 + 6 of 60. 



For methods for ascertaining melting-points see Kissling, 

 Chem. Centralb. ii, 1901, p. 507. 



152. Overheated Paraffin. SPEE (Zeit. wiss. Mik., ii, 1885, p. 8) takes 

 paraffin of about 50 C. melting-point and heats it in a porcelain capsule 

 by means of a lamp until it has become brownish-yellow, and after 

 cooling shows an unctuous or soapy surface on being cut. This mass 

 may be obtained ready prepared from Griibler. The object of this pre- 

 paration is to make the mass stickier, in view of cutting ribbons. 



VAN WALSEM (Verh. Akad. Wetensch. Amsterdam, 1899, p. 132) still 

 recommends the addition of 5 per cent, of yellow wax to paraffin of 52 

 to 57 melting-point (for large sections of central nervous system). 



JOHNSTON (Journ. Appl. Micr., vi, 1903, p. 2662) adds 1 per cent, of 



