534 THE POPULAR SCIENCE MONTHLY. 



half as thick, the greater diameter being horizontal. The hole in these 

 was quite small, and closed abruptly at the end. Fig. 2 is peculiarly 

 striking, and seems quite different in form from any yet described. 

 These " bulbs " are said to correspond with the stratification in the sand. 



Concerning the microscopic and chemical properties of the fulgu- 

 rite, little seems to have been done until within a comparatively recent 

 period. In 1875, Harting* examined some fulgurites found in acorn- 

 field at Elspeet. He describes these as vitrified tubes, having a form 

 scoriaceous, rough, and very irregular. Exteriorly they were coated 

 with sand and carbonaceous particles, while interiorly they were of a 

 white glass which was sometimes streaked with brown or black, a 

 coloration which he judges to be due to distillation products from the 

 vegetable matter in the sand. A complete chemical analysis of the 

 fulgurite yielded results as follows : SiO a , 90*2 per cent ; Al 2 O s , - 9 

 per cent ; Fe 2 3 , 0.7 per cent ; CaO, 0*1 per cent ; MgO, - 5 per cent ; 

 K s O, - 5 per cent ; NaO, 0'6 per cent ; insoluble in HC1, # 9 per cent ; 

 carbonaceous matter, 5*6 per cent. 



Discussing the results, the author argues that the alkalies and other 

 bases, belonging to the vegetable matter, have been driven off by the 

 heat of the flash, since the percentages shown are not greater than is 

 contained by the sand itself. He also conceives that the presence of 

 these bases may have aided in the reduction of the refractory silica — 

 an idea which seems to have also been adopted by Giimbel and Wich- 

 mann. When, however, we consider the extraordinary brief duration 

 of the flash and heat, this reaction seems scarcely possible. 



Giimbel f describes fulgurites from the Libyan Desert between 

 Dachel and the Ammon Oasis, in which the tube-wall consists of an amor- 

 phous glass enveloping un fused quartz-kernels. A partial chemical 

 analysis led him to conclude the interior lining to be a true quartz glass. 

 To this conclusion Wichmann \ takes exceptions. This gentleman pul- 

 verized portions of the fulgurite tubes from Senner Heide, from Els- 

 peet, and from Starczynow, and by means of a solution of great den- 

 sity # succeeded in separating the glass of the fulgurite from the in- 

 closed sand. Chemical analysis of this yielded silica as follows : 



Senner Hcide , 96-44 per cent. 



Elspeet 9426 " " 



Starczynow 9123 



*" Annales des Mines," vol. viii, 1875, p. 700. 



t " Zeit. der deutsch. geol. Gesell.," vol. xxxv, p. 648. 



\ " Zeit. der deutsch. geol. Gesell.," vol. xxxv, p. 849. 



* The solution in common use by lithologists, for separating finely powdered minerals 

 of different specific gravities, is a saturated solution of the iodides of mercury and potas- 

 sium. Properly prepared this can be brought to a density sufficient to float any substance 

 of specific gravity not greater than 3 - 25. By gradually diluting the solution and thus 

 rendering it less dense, it is possible to separate the various minerals of a powdered rock 

 with a considerable degree of accuracy. 



