98 



CHEMISTRY. 



Cliuiiu, 



pared by that philosopher. This liquid it little else than 

 hydrosulphurct of ammonia holding an excels of ammo- 

 ma in solution. 



Sp. 7. Hijilioitilphurri of Magnesia. This substance 

 may be formed, by passing a current of sulphureted hy- 

 drogen through water in which magneaia is diffused. Its 

 properties have not been hitherto examined. 



Sp. 8 andi>. llydrotulphurcts ttf (.Huciiut and of Yllria. 

 JIM! Yttria. From the experiments of Klaproth and Vauquelin, we 

 know that the hydrosulphurets do not precipitate glucina 

 or yttria from acids. Hence it is likely that they are 

 capable of combining with sulphureted hydrogen, though 

 these combinations have not hitherto been examined by 

 chemists. 



ihcr alumina nor zirconia combine with sulphuret- 

 ed hydrogen. Hence the hydrosulphurets precipitate 

 these earths from acids. 



When the alkalies and alkaline earths arc mixed with 

 sulphur and water, and boiled in a glass vessel, a brown 

 coloured solution is obtained, formerly called lii/iiiri Ih'i-r 

 of sulphur. At present the term hudrogurcted sidphur- 

 rts is applied to these solutions. They are conceived to 

 be combinations of the alkaline bases with sulphur and 

 sulphureted hydrogen at once, and therefore to be triple 

 compounds. The proportion of sulphureted hydrogen 

 is often very small. 



The hydrosulphurets precipitate almost all the metals 

 from their solutions. The precipitates vary in their co- 

 lour according to the metal. The following Table exhi- 

 bits a view of the colours of the various precipitates in 

 these cases, as far as the subject has been investigated. 



CHAP. V. 

 OfSoapt. 



THE fixed oils have the property of combining with 

 alkalies, earths, and metallic oxides, and of forming a 

 claw of compound* whicii have received t'u- name of 

 SOAPS. A these soaps off. r from each other very ma- 

 terially, according as their base it an alkali, an earth, or 



a metallic oxide, it will be proper to eoitider each let ' 

 separately. 



I'lu 



SECT. I. Of Alkaline Soaps. 



All or most of the fixed oils arc capable of combining Alkaline 

 with the alkalies, and forming soap ; but the differences opw 

 which they produce on the qualities of the soap have on- 

 ly been observed in a few cases. We can only consider 

 the different species occasioned by different alkali 



Sp. 1. Soap of Soda, or Hard S>xi]\ The word sodji 

 (tapo, <r*ttn) first occurs in the writings of Pliny and 

 Galen, and was obviously derived from the old German 

 word*(yjf: for the knowledge of this useful compound 

 seems first to have arisen among the Gauls and Germans. 



Hard soap is made by mixing soda of commerce with 

 a sufficient quantity of lime and water to deprive it of its 

 carbonic acid, drawing off the ley, and boiling it with a 

 quantity of olive oil or tallow, amounting to six timc. 

 thc weight of the soda used. When sufficiently boiled, 

 a quantity of common salt is added, which induces the 

 soap to separate from the water, and to float upon the 

 surface. Though in this country, where kelp is usually 

 employed at least in part to furniah the soda, the quan- 

 tity of common salt present from the beginning is usually 

 sufficient without any addition. The soap is then pour- 

 ed into proper vessels, and when cold cut into parallele- 

 pipeds. Whale oil has been tried, but found improper 

 for making hard soap. In this country, tallow is usual- 

 ly employed. In France, and the south of Europe, 

 olive oil is used. When oil or tallow alone is used, the 

 soap has a white colour ; but it is usual to add a quan- 

 tity of rosin, which gives it a yellow colour, and a softer 

 consistence. It is then called yrllon- soap. 



The appearance and properties of common soap are so 

 well known, that it is unnecessary to describe it. The 

 various uses to which it is applied are equally well known. 

 It dissolves in alcohol, but is precipitated by the addition 

 of water. With water it readily mixes, though it doe 

 not, strictly speaking, dissolve in that liquid, as most of 

 it is separated by the filter. A specimen of white soap 

 analysed by Darcet, Lelievre, and Pelletier, was compo- 

 sed of 60.94 oil, 



8.56 alkali, 

 30.50 water. 



100.00 



Sp. 2. Soap of Potash, or Soft Soap. When potash 

 is substituted for soda, the soap never hardens by cooling, 

 but remains always soft. Whale oil is said to be em- 

 ployed in the manufacture of soft soap. A little tallow 

 is also added, which, by peculiar management, is disper- 

 sed through the soap in fine white spots. The proper- 

 ties of soft soap are too well known to need description. 

 It is the only species of soap with which the ancients were 

 acquainted. It is but little used in this country in com- 

 parison of hard soap. 



Sp. 3. Soap of Ammnnia. This soap may be formed 

 by digesting carbonate of ammonia on soap of lime. Its 

 taste is more pungent than that of common soap. It 

 mixes sparingly with water, but is pretty soluble in alco- 

 hol. The substance employed as an external application 

 by surgeons under the name of volatile liniment, is scarce- 

 ly any thing else than this soap. 



SECT. II. Of Earthy Soaps. 



The earthy soaps differ essentially from the alkaline, Earthy 

 in being insoluble in water, and therefore incapable of wap- 



