174 Jounston-Lavis—The Eruption of Vesuvius in April, 1906. 
the composition is sensibly the same as that of the newest lava, except that the 
iron is more peroxidized ; exactly what we should expect. The differences 
between the insoluble constituents of the two-coloured dust are only nominal. 
When we examine, however, the soluble saline part, we find that the salts of the 
cocoa-coloured dust contain 4 per cent. more Na, but 23 per cent. less K, than 
the grey dust. Ca also is more than 1 per cent. less in the red than the grey dust, 
whereas the former is poorer in SQ, and richer in Cl. 
As will be seen by the appended analyses,* the salts of the new lava are very 
different in composition from those of the dusts. Carbonates predominate in the 
lava, and chloride in the dusts. 
HCl. H2S80u. 
100 grammes of grey dust contain 3 0 . 0:00219 0:00294 
100 grammes of cocoa-coloured dust contain . 0:00109 0:00145. 
Only the faintest traces of sulphurous acid were found. 
; | | Sol. Salts | 
a oat oe cua | fet | Sey | intara ot 
Na Clea 49:158 44°300 Ca oe Be 8°399 9°334 0:945 
WE 5 6 6 5°110 6:964 Mg shen 1°292 1:759 -— 
WOK 5G 6 6 1:494 1°559 K ae 3°768 6:048 12-758 
CASO, 0 6 6 27:198 31:731 Na Pare 22°116 18:047 80°395 
UGSKOn o o 8°399 13°488 Mn Sotees ieee 0:657 0-681 — 
WESIO, 6 o 8°557 1°927 Cl ae 34°520 32:977 20:1386 
SiO ane 0:079 0:026 SO, o 0 0 29°520 31:150 4:723 
SS ‘SO, 6 6 0:079 0:026 —_ 
Total . 99:995 99:995 COR nites — —_ 30°749 
Total . {| 100°351 100-022 99:995 
Dried at 180°C., the red dust contained 5 : . 3240 per cent. of salts. 
3 or the grey dust contained . é : 5 PGI - 5 
6 5 the lava of Boscotrecase contained . . 0:395 x 
These salts are probably derived from sublimates in the interstices and fissures 
of the cone, which a careful observer may watch continually being deposited from 
the escaping vapours of the magma occupying the chimney. In fact, this saline 
constituent represents the pulverized remains of the halite, sylvite, erythrosiderite, 
* Casoria, Prof. E., op. edt. 
