156 AMYGDALIN 



cations of ita presence by tho usual reagents until after the addition of nitric acid ; 

 and it is curious that thoro likewise exists a red compound of this class in which the 

 iron exists in the state of perchloride similarly marked, in fact as NH 4 C1, Fe'Cl 3 . 



A very simple method of removing tho iron, suggested by Mr. Brewer, consists in 

 passing a few bubbles of chlorine gas through the hot concentrated solution of the 

 salt, by which the protochloride of iron is converted into the perchlorido. 



2FoCl + Cl = Fo 2 Cl s . 

 ZFeCl + Cl 2 = Fe'Cl". 



The free ammonia always present in the solution decomposes this perchloride with 

 precipitation of sesquioxide, and formation of an additional quantity of sal-ammoniac. 

 Fe 2 Cl 3 + 3NH 4 = Fe* s + 3NH 4 Cl. 

 re-Cl" + 3(M-H 4 ) 2 O = Fe 2 s + 



The sesquioxido of iron, which is of course present in the form of a brown hydrate, 

 is filtered off or separated by docantation, and a perfectly pure solution is obtained. 



The only precaution necessary is to avoid passing more chlorine than is requisite 

 to peroxidiso tho iron, since the ammonia salt itself will bo decomposed with evolution 

 of nitrogen, and the dangerously explosive body, chloride of nitrogen, may result 

 from the union of the liberated nitrogen with chlorine. 



Uses. The most important use of sal-ammoniac in the arts is in joining iron and 

 other metals, in tinning, &c. It is also extensively used in tho manufacture of am- 

 monia-alum, which is now largely employed in the manufacture of mordants instead 

 of potash-alum. A considerable quantity is also consumed in pharmacy. 



Sal-ammoniac is one of those salts which possesses, in a high degree, the property 

 of producing cold whilst dissolving in water ; it is, therefore, a common constituent 

 of frigorific mixtures. See FREEZING MIXTURES. . 



AMMONIUM, SULPHIDES OF. When sulphuretted hydrogen gas is passed 

 into a solution of ammonia in excess, it is converted into tho double sulphide of 

 ammonium and hydrogen or, as it is frequently called, the hydrosulphate of 

 sulphide of ammonium. NH 4 S, HS (MTH 1 , HS). 



This solution is extensively employed as a re-agent in tho chemical laboratory, for 

 tho separation of those metals the sulphides of which are soluble in acids viz. nickel, 

 cobalt, manganese, zinc, and iron, which are precipitated by this reagent in alkaline 

 solutions. 



By exposure to the air, the hydrosulphuric acid which it contains is decomposed, 

 the hydrogen being oxidised and converted into water, whilst tho liberated sulphur 

 is dissolved by the sulphide of ammonium, forming the bisulphide, or even higher 

 sulphide. 



This solution of the polysulphido of ammonium is a valuable reagent for dissolving 

 the sulphides of certain metals, such as tin, antimony, and arsenic, tho sulphides of 

 which play tho part of acids and form salts with tho sulphide of ammonium. 



By this deportment with sulphide of ammonium, these metals are separated, both on 

 the small scale in tho laboratory, and also on tho large scale, from the sulphides of 

 those metals such as lead, copper, mercury, &c. the sulphides of which are insoluble 

 in sulphide of ammonium. 



The higher sulphides, viz. the tersulphide and the pentasulphido, are bodies 

 of purely scientific interest. They are obtained by distilling tho corresponding sul- 

 phides of potassium with sal-ammoniac. 



All the sulphides of ammonium are soluble in water without decomposition. 



Ammonia combines with all the inorganic and organic acids, but for an account 

 of these compound bodies we must refer to "Watts's ' Dictionary of Chemistry,' as they 

 have but few applications in the arts and manufactures. 



AMORPHOUS. (Privative &, destitute of ; popf)], shape : without s/Mipe). Said 

 of mineral and other substances which occur in forms not easy to bo defined. This 

 term may be regarded as the opposite of crystalline. Some elements exist in both 

 the crystalline and the amorphous states, as carbon, which is amorphous in charcoal, 

 but crystalline in the diamond. 



Tho peculiarities which give rise to these conditions evidently depending upon 

 molecular forces which have not yet been defined present one of tho most fertile 

 fields for study in tho range of modern science. 



AMYGDALIN. C 40 H" NO 22 + 6 HO. (C 2 H 27 M'0 11 + 3H 2 0.) A peculiar 

 substance, existing ready-formed in bitter almonds, tho loaves of the cherry-laurel, 

 the kernels of the plum, cherry, peach, and the leaves and bark of Primus i^adus, and 

 in the young sprouts of the P. domestica. It is also found in tho sprouts of several 

 species of Sorbns, such as S. aucuparia, 8. torminalis, and others of the same order. 

 To prepare it, tho bitter almonds are subjected to strong pressure between hot plates 



