BAILEY. | Chemistry of Plasters. 163 | 
duces a considerable quantity of dust, which deposits all over 
the upper parts of the building, and on the vegetation near by. 
In some of the best mills this dust is collected and saved. _ 
This process has been briefly described, in order to refer to 
some experiments that have been made on the composition of 
the plaster at different stages of its manufacture. Two com- 
plete sets of material from different plants have been secured, 
and analyses of these have been made. Samples taken April 4, 
ISDA 2 ; 
COMPOSITION OF PLASTER AT DIFFERENT STAGES OF MANUFACTURE. 
No. 1, No. 2, No. 3, No. 4, No, 35, 
crude. finished. dust. tailings. set. 
Silica and insoluble résidue..... 1229 144 Bul 13.48 22.06 12083 
Tron and aluminum oxides ...... BY 2.16 D sO. 3 eG? 
Calciumioxidemaae ae 29.67 33) DS Oma 32 US 30.05 
Miaronvesiunmyo xd Gl Cyaan na sien 0.78 ORO: ORS9 0.56 0.61 
Sulphuric anhydride............ 34.87 39.85 40.03 33.06 30.73 
(OMiMoo CHOEACID 5 oo dcccoucdoscacus 33 . a) ab UL OB Lari ae) 33ND) 
NU WUE ss oi emetic Meanie ON ie a a aa 16.07 4.91 6.78 4.43 16.38 
MO Gal Siete ike et ae A Mio 99.47 99.78 98.79 99.82 99.97 
The most probable combination is as follows: 
No. 1, No. 2, No. 3, No. 4, No. 5, 
crude finished. dust. tailings. set. 
Silica and insoluble residue..... 12}, HY) 4b Ssh 13.38 2424 OPH 12} OB 
Iron and aluminum oxides....... Dh AAT MS Dh 05 2 LDS 1.62, 
Magnesium carbonate........... 18 91 .59 .56 61 
Calciumuacarbonatesw eae eee 8.01 9.42 6.53 13.107 8.07 
CalGntniam OGIE oo o60060 o006 does be DH IP 185 2.56 4.70 1.89 
Calciumysulpitateneane eee ee 57.95 66.22 66 .52 53.67 59.37 
WEA CTA tNer sees ce ium nS 4 RSA PRON 16.07 4.91 6.78 4.43 16.38 
Mortals ae Nn ater es 99.49 | 99.78 | 98.79 | 99.78 | 99.97 
In this case the determination of carbonic anhydride was 
carefully made in each sample, and it is interesting to notice 
that this confirms the opinion already expressed, that there is 
not enough carbon dioxide and sulphuric acid to unite with the 
bases present. In other words, the hydrochloric acid used to 
dissolve the mineral decomposes something besides the sul- 
phates and carbonates, namely the silicates. If the iron is 
