THE AMERICAN 



MONTHLY 



MICROSCOPICAL JOURNAL. 



Washington, D. C, January, 1884. 



Vol. V. 



No. 1. 



The Microscopical Study of the 



Crystallizjitiou of Allo- 



tropic Sulphur. 



Not long ago, while melting some 

 sulphur for the purpose of obtainiiig 

 the flexible form of that substance 

 suitable for taking impressions from 

 a coin, I became interested in the 

 phenomena observable on cooling the 

 melted material, and watching the 

 recrystallization under the micro- 

 scope. Having shown these appear- 

 ances to a nvmiber of friends, and 

 found no one to whom it was not 

 new, it seems worthy a description 

 in the Journal. 



Next, perhaps, to phosphorus, sul- 

 phur is the most remarkable and in- 

 teresting element in the allotropic 

 forms it presents. Chemists and 

 physicists describe at least six differ- 

 ent allotropes of sulphur, but their 

 study presents many difficulties, since 

 only a few of them are as yet well 

 identified and characterized. ( Wurtz, 

 in Johnson's Universal Cyclopaedia.) 

 Two of these forms are said to be 

 crystalline, crystallizing in different 

 systems, and being, therefore, di- 

 morphs. These are — i , right rhom- 

 bic octahedra, and 2, oblique rhombic 

 prisms belonging to the monoclinic 

 system. The description of the char- 

 acteristics of the different forms may 

 be found in the text-books, and the 

 only one necessary to be referred to 

 here is the singular product obtained 

 by heating sulphur till it passes from 

 a yellow fluid to the state of a brown 

 viscid mass (at about 230° C), and 

 then suddenly cooling it by pouring 

 it into cold water. Sulphur thus 

 treated loses its prominent charac- 



teristics, and remains for some time 

 flexible, retaining its dark color, and 

 may be moulded like wax, readily 

 taking impressions like that sub- 

 stance. 



Flow^ers of sulphur or roll-sulphur 

 may be convenientl}- melted in a por- 

 celain capsule, over a lamp or in a 

 stove, until the brown color appears. 

 It is then poured into cold water, and 

 the mass again melted, and a few 

 drops poured on a slide. It hardens 

 rapidly, and must be kept liquid 

 while a thick cover is pressed down 

 upon it. Before it again congeals it 

 is placed on the stage of the micro- 

 scope, and examined with a power 

 of 75 or 100 diameters. As it cools, 

 beautiful masses of prismatic crystals 

 start from the edges of the film, and 

 spread over the field with a rapidity 

 proportionate to the time occupied in 

 cooling and the thickness of the film. 

 With a thick cover, or with what is 

 still better, a piece of a thin slide, for 

 a cover-glass, cooling proceeds slowly 

 enough to enable the forms of the 

 crystals to be studied as they grow. 

 The warm stage is also an advantage. 

 They may be re-fused, and the same 

 process observed an indefinite num- 

 ber of times, an endless variety of 

 form and color being obtained by the 

 different recrystallizations. 



A Bunsen burner affords the most 

 convenient means of heating the slide, 

 but a spirit-lamp, German student- 

 lamp, or a hot stove may be em- 

 ployed, care being taken to apply the 

 heat gradually, and to distribute it 

 by constantly moving the slide to 

 avoid cracking. The odor of the 

 melting sulphur is disagreeable to 

 some persons, and care should be 



