Aua. 19, 1923 AUROUSSEAU: RESIDUE FROM SILICA 331 
analyses of different modifications of the rock were executed. They 
indicated only the slightest variation in composition, any one of them 
being quite representative of the rock. These results will doubtless 
be published elsewhere, and therefore the average of the three will be 
used here. In addition, a number of determinations of ferrous and 
total iron were made on the same material, the latter providing the 
residues examined. - 
Three portions, amounting to 3.0008 grams, of rock powder pro- 
vided 0.0165 gram of residue. This was obtained by three separate 
fusions, carried out under identical conditions. Nevertheless, the 
third fusion, judging from the appearance of the residue, was not as 
effective as the others. After expelling the hydrofluoric and sul- 
phurie acids, the residues were ignited for an hour in the electric 
furnace at a temperature of 850°C., in an oxidizing atmosphere. They 
were collected, after weighing, by ordinary sodium carbonate fusion, 
and were analyzed in the usual way, except for the deviations required 
for MnO and P.O;. The composition of the residue by weight was 
found to be as follows: 
grams 
SNE SiR A Band ees Sil Sinan Ne eR Sen tS 2). nl Ses BRN Nae oyenS at 0.0021 
FeO; SST Eee b fetex SIE isi atie's eicuchiby cle les on6 a1n.@ & @. ao) eta © ale teehee ais el Ses. a wim ipo uaie 0.0041 
COUT Oar ACM GM sien: Sache leit ie a ee a ne BA re Pear eoe etio oe 0.0003 
[8,10 apa Bie ae aa os 0 Se a a 2 = FS Oe aa eae 0.0026 
TiO, SiS Shee Ree BE, SE rE eR ROL ae MERCER TD ch or 8 tic Shc ho eters CMON a CMEC RC Cae: 0 .0049 
Ora. eer atts cs coc iechc ce os 38 AE Eee Tae ers crcer era 0.0003 
1A rat Yi eee es se tk ane eS a in FN a none 
PS) GAR EES Be ae Renee ee RE MORT Ceeee I Ee lao Sosy ee Neen 0.0013 
| Dao lS retin cou a ve yc yee ee ame yc ae a TENS G6 UL nee ere 0.0009 
Aigypsile reg a: RAL RY, Are a eS er ie cee sar. 6 ein oS emegr 0.0165 
The residue thus consists principally of the oxides of titanium, iron, 
magnesium, and aluminium. The quantity of MgO and the presence 
of SO; are somewhat surprising. 
The interest and significance of the composition of the residue, for 
the analyst, lies in its relation to the composition of the rock. Ona 
percentage basis, the constituents determined amount to 0.52 per cent 
of the rock (column 2, table 1). If the amount of each oxide in the 
residue be compared with the amount of the corresponding oxide in 
the rock, it is evident from column 3 of table 1 that Ti0., MgO, 
and Fe.O; (the relation is to total iron) have here shown the greatest 
tendency to remain behind in the residue. It is to be noted that only 
a negligible proportion of the P.O; remained behind, and relatively 
little alumina. The subjoined table expresses the results clearly. 
