CHEMISTRY. 



Element* permanent salts with the salifiable bases. When the 

 ' alkalies are dropt into a solution of gallic acid, it as- 



u ^l sumes a green colour. When the liquid is evapora- 

 ted, the acid seems to be decomposed. Gallic acid 

 occasions a blue or a red colour, when dropt into 

 lime, barytes, or strontian water. 



GENUS XVIII. Prussialef. 



Prussiate*. The prussic acid combines with the salifiable bases, 

 but the compounds have little permanency, as the 

 acid is separated by mere exposure to the air, or by 

 a heat of 120. Hence these salts have been but 

 little examined. It is capable of combining with an 

 alkali or earth, and with a metallic oxide at the same 

 time, and of forming triple salts, which have a great 

 deal of permanency. The oxide of iron is the me- 

 tallic oxide usually present. Of all these salts, the 

 most important is the prussiate qfpotaift-and-iron, or 

 the triple prussiate of potash, as it is in common use 

 as a re-agent. It crystallizes in cubes or parallelopi- 

 pedi. It has a yellow colour, and is semi-transpa- 

 rent. It contains about one-fourth of its weight of 

 oxide of iron. It has a bitter taste, and is insoluble 

 in alcohol, though soluble enough in water. 



SECT. II. Of Metalline Salts. 



Of metal- Acids combine only with the oxides of metals: 

 tine talu. they seem incapable of uniting with metals them- 

 selves. Now most metals form more than one oxide, 

 and acids are usually capable of combining with two 

 oxides at least of the same metal. The properties of 

 the rait vary a good deal according to the state of 

 oxidizemcnt of the oxide. Thus muriatic acid com- 

 bined with the protoxide of mercury, foims a salt in- 

 soluble in water, and which acts merely as a cathartic 

 when taken internally. The same acid, combined with 

 the peroxide of mercury, forms a salt which is soluble 

 in water, and constitutes one of the most virulent poi- 

 sons known. To distinguish the state of oxidizement 

 of the metal in these salts therefore is necessary. At 

 present we shall satisfy ourselves with denoting those 

 metalline salts that contain protoxides by the usual 

 name ; while to the names of those that contain a 

 peroxide, the syllables oxif will be prefixed. Thus 

 mUiate of mercury is the compound of sulphuric 

 acid and protoxide of mercury ; oiysulphtite of mer- 

 cury ia the compound of the same acid, and peroxide 

 of mercury. As there are twenty-seven metals, it is 

 obvious that the genera of metalline salts are twenty, 

 seven. 



GENUS I. Kails of Gold. 



Salt* of The salts of gold are soluble in water, and the so- 



gold, lution has a yellow colour. Triple prussiate of pot- 



ash occasions a white precipitate in them, and the 

 infusion of nutgalls gives them a green colour, and 

 occasions a brown precipitate which is gold reduced. 

 A plate of tin or muriate of tin occasions a purple 

 precipitate. Sulphate of iron precipitates the gold 

 in the metallic state. 



Sp. 1. Muriate of Gold. This salt is easily ob- 

 tained by dissolving gold in a mixture of one part 



nitric, and four parts muriatic acid. The solution Elements 

 takes place speedily, and with effervescence. It has ' 

 a yellow colour, and when sufficiently concentrated, ._ e ' _,' 

 lets fall small yellow crystals of muriate of gold. 

 They are four-eided prisms or truncated octahedrons, 

 and exceedingly deliquescent. The taste of this salt 

 is acerb, with a little bitterness. It tinges the skin 

 of an indelible purple colour. It dissolves readily 

 in alcohol, and seems more soluble in ether than in 

 water. Almost all the metals throw down the gold 

 from this salt, either in the metallic state or in that 

 of a purple oxide. Hydrogen, phosphorus, and 

 sulphurous acid, produce the same effect by depriv- 

 ing the gold of its oxygen. Muriate of tin occasions 

 a beautiful powder, called purple of casiius. It is 

 employed as a paint, and to give a red colour to glass 

 and porcelain. According to Proust, it is a com- 

 pound of three parts of the oxide of tin, and one 

 part of gold, in the metallic state. But it seems 

 more likely that the gold is in the state of protoxide. 



Sp. 2. Nitrate of Gold. Nitric acid, containing 

 a considerable proportion of nitrous gas in solution, 

 dissolves gold, especially if it be much divided, as is 

 the case in gold leaf. The solution has an orange 

 colour, and cannot be evaporated to dryness without 

 decomposition. 



The other salts of gold hare not hitherto been 

 examined. 



GENUS. II. Salts f Platinum. 



The solution of these salts in water has a brown s * 11 ? of 

 or yellowish brown colour. No precipitate is pro- ^ a 

 duced by prussiate of potash or infusion of nutgalls. 

 Sal ammoniac occasions a copious yellow-coloured 

 precipitate. 



Sp. 1. Nitrate of Platinum, Nitric acid does not 

 act upon platinum., but it dissolves its peroxide, and 

 forms a salt not hitherto examined. 



Sp. 2. Muriate of Platinum. This salt is obtain- 

 ed by dissolving platinum in aqua regia, and evapo- 

 rating the solution, which is of a dark brown colour 

 and opake. Small irregular crystals of muriate of 

 platinum may be obtained, not more soluble in water 

 than sulphate of lime. This salt has a disagreeable 

 astringent metallic taste. Heat drives off the acid, 

 and reduces the oxide to the metallic state. 



The properties of the remaining species have been 

 but imperfectly examined. Potash and ammonia arc 

 capable of combining with the salts of platinum, and 

 forming compounds very little soluble in water. 

 Hence a precipitate takes place when these alkalies 

 are poured into solutions containing platinum. 



GENUS III. Salts of Silver. 



The nitric is the only acid which dissolves silver Salts of 

 with facility, but they all combine with its oxides si 'ver. 

 and form salts, most of which are but sparingly so- 

 luble in -.vater. When the salts of silver are exposed 

 to the action of the blow-pipe on charcoal, a globule 

 of silver is obtained. Muriatic acid, or a muriate, 

 occasions a white precipitate in their solutions, which 

 becomes black when exposed to the light. The 

 prussiates occasion a white precipitate, and the hy- 



