53 
and somewhat deliquescent in moist air; hence the percentage of arse- 
nic is somewhat uncertain. The nesv preparation is permanent in dry 
air. The hydrous sodium arsenate contains dO.d per cent of water; 
hence, a given weight of this substance will contain but little more 
than half as much arsenic as an equal weight of the exsiccated. The 
average dose of the latter is accordingly placed at about one-half that 
of the former. 
Dose. — “Average dose: 0.003 Gm. = 3 milligrammes (gV grain).'’ 
(U. S. P.) 
SODII CARBONAS 3I0X0HTDRATUS. 
3Iouoliydrated Sodium Carbonate. 
XaXOs-HoO 
Sodii Carbonas and Sodii Carbonas Exsiccatus (U. S. P. , 1890) are 
dismissed from the Pharmacopoeia and the monohydrated salt intro- 
duced. 
The Sodii Carbonas contained ten molecules of water of crystalliza- 
tion or 63 per cent: part of this Avas lost on exposure to air, so that 
the salt was of uncertain strength. The Sodii Carbonas Exsiccatus 
contained about 26 per cent of water and probably corresponded to 
the formula Aa^COg -j- 2H._,0. This salt was somewhat hygroscopic. 
The monohydrated salt does not effloresce at ordinary temperatures, 
nor does it absorb much moisture. It is therefore more uniform in 
composition than either of the others. 
Character. — A white, crystalline, granular powder, odorless and hav- 
ing a strong alkaline taste. It is somewhat less soluble than Sodii 
Carbonas (U. S. P., 1890), but more so than Sodii Bicarbonas. 
Solubility. — Soluble in Avater (1:2.9), in boiling water (1:1.8), in gly- 
cerin (1:8); insoluble in alcohol. 
Dose. — ‘'AA'erage dose: 0.250 Gm. = 250 milligrammes (1 grains).” 
(U. S. P.) 
SODII CITEAS. 
Sodium Citrate. 
2 ya 3 C 6 H 50 ,-fllHoO 
Properties. — A white, granular powder, odorless. It slowly efflo- 
resces on exposure to dry air. Soluble in 1.1 parts of cold Avater and 
in 0.1 part of boiling water; slightly soluble in alcohol. 
Dose. — “Average dose: 1 Gm. (15 grains).*' (U. S. P.) 
A carbonated solution of Sodium Citrate is contained in the National 
Formulaiy under the name of Liquor Sodii Citratis and in the German 
Pharmacopoeia under the name Potio RiveG 
