3§9 
^infrequently fome portion of iron is contained in the mafs ; it is 
therefore to be confidered as more or lefs a compound, and its good* 
nefs is to be eftimated accordingly. The Spanifh Soda, of the beft fort, 
Is in dark coloured maffes, of a bluilh tinge, very ponderous, fono 
rous, dry to the touch, and externally abounding with fmall 
hout any offenfive fmell, and very fait to the tafte ; if long 
expofed to the air, it undergoes a degree of fpontaneous calcination. 
The beft. French Soda is alfo dry, fonorous, brittle, and of a deep 
blue colour, approaching to black. The Soda, which is mixed with 
fmall ftones, which gives out a fetid fmell on folution, and is white, 
foft, and deliquefcent, is of the worft kind.* 
The method of purifying this fait is directed in the London Pharm, 
under the article of Natron prseparatum, and in the Edinburgh Pharm. 
under that of Sal aikalinus fixus fofftlis purificatus : the pure cryftals 
thus formed of Alicant barilla, are colourlefs, tranfparent, lamellared, of 
» 
a rhomboidal figure, and one hundred parts are found to contain 
twenty of alkali, fixteen of aerial acid, and fixty-four of water ;° but 
upon keeping the cryftals for a length of time, if the air be not 
excluded, the water evaporates, and they alTume the form of a white 
powder. According to Imlin, p one ounce of water, at the temperature 
62 of Fahr. diffblves five drams and fifteen grains of the cryftals. J 
The fame author alfo found that this fait preferved flefh from putridity 
longer than common fait, though not fo long as the vegetable alkali. 
Natron has been thought ufeful in fcrophulous diforders, but it is 
feldom given in its fimple ftate. 
In combination with vitriolic acid this alkali forms Glauber fait, 
or Natron vitriolatum ; with nitrous acid, cubic nitre ; with marine 
", common fait ; with the fedative fait of Homberg, borax ; with 
cream of tartar, Rochelle fait, or fel faignette. 
To enter fully on the peculiar properties, or chemical qualities, of 
this alkali, would lead us too far, and is properly the province of 
chemiftry. It is in common ufe in the manufacture of glafs and foap, 
* For this, and almoft the whole on this fubjeft, we are obliged to the late Profeflbr 
Murray. See his App. Med. vol. 4. 
? Bergman in Scheffers. p Dljf. de Soda. t . „. 
X Kirwan fays, 2, 5 times its weight of water at this temperature are required 
mm. p. 1 "' 
No 
G 
and 
