THE AMERICAN MONTHLY 



[January, 



taken not to inhale the fumes di- 

 rectly. The brass-work of the stage 

 should be also guarded from contact 

 with the melted sulphur. If the 

 brass is accidentally discolored, how- 

 ever, a little ammonia on a cloth re- 

 moves the black stains readily. The 

 fumes alone exercise little influence 

 on lacquered brass. 



The study of these crystals as they 

 form with mathematical regularity of 

 outline, yet constantly modified by 

 encroachment on one another, is one 

 of the most fascinating occupations to 

 a microscopist. Their appearance 

 must be seen to be understood, as a 

 verbal description entirely fails to 

 convey an idea of their beaut}'. Long, 

 straight lines shoot like an arrow into 

 the surrounding fluid, throwing out 

 laterally as they go countless subor- 

 dinate prismatic crystals, or some- 

 times the main axes spread by vast 

 numbers of delicate plates, with ab- 

 solutely regular outline, a right-angled 

 border generally presenting in the 

 line of direction. These slide one 

 over another, as the different strata 

 are cooled, and finally leave the whole 

 thickness of the film fixed in a dense 

 crystalline mass, suggestive of a sec- 

 tion of granite or porphyry. 



When we remember that sulphur 

 in its mineral form is itself a volcanic 

 product, the analogy of the results pro- 

 duced by its hardening, after fusion, to 

 the internal structure of igneous and 

 metamorphic I'ocks is the more inter- 

 esting. After remaining for several 

 days on the slide the crystals often 

 undergo spontaneous fracture, show- 

 ing cleavage lines similar to those 

 found on a great scale in the earth's 

 crust, and here and there a vivid sug- 

 gestion of basalt. This contraction 

 sometimes produces concentric cracks 

 immediately after cooling, when a high 

 degree of heat has been applied, or 

 after numerous regelations. These 

 cracks have a remarkable symmetrv 

 of arrangement, and are first concen- 

 tric and afterward followed by radial 

 ones. 



Returning to the first changes de- 



scribed, the prismatic and plate- 

 shaped crystals, by their junction 

 with crystals from other centres of 

 crystallization, form the most unique 

 combinations imaginable. The long, 

 straight lines produced by the axes of 

 the different crystalline masses are 

 often so connected by lateral lines as 

 to convey a striking likeness to rude 

 architectural forms and sculptured 

 ornaments. When the film is thick 

 the crystals rush together at various 

 angles like opposing lines of bayo- 

 nets, and by their blending form an 

 apparently homogeneous mass which 

 flows like lava across the field, its 

 advancing edge showing numberless 

 wave-like wrinkles. When two such 

 masses meet at an angle they join and 

 advance together, leaving the line of 

 their union clearly marked out by a 

 straight line, such as often appears in 

 intersecting veins of agate. Some- 

 times crystals start from independent 

 centres in the fluid, producing ro- 

 sette-shaped masses of much beauty. 



It should be observed that while 

 the phenomena described above are 

 the rule, it occasionally happens that 

 after the first melting a very rapid 

 congelation takes place, leaving a 

 nearly structureless appearance of the 

 whole field. All that is then neces- 

 sary is to rewarm the slide and press 

 the cover lightly, when the crystals 

 will appear as here described. 



Under the polariscope a thin film 

 of sulphur in its allotropic state often 

 shows very rich prismatic colors, and 

 the mineral therefore deserves a place 

 in the fii^st rank of polariscope ob- 

 jects, though not included in the very 

 full list given in the latest edition of 

 Carpenter. 



A brilliant red or green local color 

 is sometimes noticed also in the crys- 

 tals wdien modified by heat. Too 

 much heat forms black crystals and 

 numerous bubbles, obscuring. the fui'- 

 ther study of the crystallization. 



In the study of this singular sub- 

 stance not the least intei'esting feature 

 is the behavior of the microscopist's 

 old friend, the air-bubble. When a 



