ciu;Mi.vn:v. 



45 



leaves thorn with a yollowiwh tinge. In those oases thui gM U 

 used. It seems simply to combine with the colouring matter, 

 thus destroying it. The gM is sometimes used for < 



ntation when it is proceeding too rapidly. This is 

 tli,> manufacture of cider, by burning sulphur orer the 

 vessel iti whirli the fermentation is proceeding. 



>ide (symbol, SO,; combining weight, 80; 



,, 40). This substance may bo prepur. I l.y parsing a 



re of sulphurous acid gas and oxygon through a tube con- 



Hpongy i>latinum heated to 180 Cent. In the pores 



of tii.- platinum the sulphurous gas becomes oxidised into SO,, 



wiu.-h passes out of the tube in white vapours, and condenses in 



vor into fine silky noodles of sulphuric anhydride. 

 '1'h is substance possesses no acid properties until it combines 

 iritli water, which it does with violence, forming sulphuric acid. 

 When the vapour of sulphuric trioxide is passed through a 

 red-hot tube it is decomposed into 2 volumes of sulpliio dioxide 

 and 1 of oxygon, thus 



SO, = SO, + O. 

 2 = 2 + 1. . 



Nordhausen Sulphuric Acid (H 2 0.2SO.,). At Nordhansen, a 

 town in Saxony, a fuming acid of the above name and formula 

 was made by distilling green vitriol, which is iron sulphate, 

 thus 



4 (FeSOJ + H a O = 2SO, + 2Fe,0, -r H a O.2SO,. 



This acid, when heated, gives off sulphuric anhydride, and 

 leaves British oil of vitriol behind, thus : 



H,O.2SO, = SO, + H a O.SO,. 



It ia capable of dissolving sulphur, but its great use is to dissolve 

 indigo, which property gives it its commercial value. 



Sulphuric Acid, or Oil of Vitriol (H.,S0 4 ). No chemical com- 

 pound is of such use in the arts and manufactures as this ; 

 . the commercial prosperity of a country may be very 

 accurately measured by the quantity of sulphuric acid it con- 

 sumes. 



mode of preparing the acid is to oxidise sulphurous acid 

 gas, by means of nitric trioxide, thus 



SO, + H,O + N a O, - H-.SO. + N-.Oa. 



Here it will be seen that the nitric trioxide gives one atom of 

 its oxygen to the S0 2 , which thus becomes SO S ; this combines with 

 an atom of water, forming H 2 OS0 3 , which is usually written 

 H a SO 4 . The N 2 0j is now N 2 3 , nitric oxide ; but in the presence 

 of steam this gas is capable of combining with oxygen and 

 returning to its former state, thus 



N,0, + O = N a O j; 



and it is again in a condition to oxidise another atom of SO 2 . 

 Thus it appears that the nitric trioxide merely acts as a carrier 

 of oxygen between the air and the sulphurous acid gas. Theo- 

 retically, a definite quantity of the trioxido can transform an 

 indefinite quantity of the sulphurous into sulphuric acid. Prac- 

 tically, however, this is impossible, for reasons which will be 

 sufficiently apparent. Fig. 47 shows the arrangement by which 

 the manufacture of sulphuric acid ia carried on. A chamber made 

 of wood, sometimes 300 feet long and 15 broad by 15 high, is lined 

 with sheet lead ; water a few inches in depth covers the bottom ; 

 at one end there is a furnace in which sulphur is burning, 

 and the flames of the sulphur heat a crucible containing sodium 

 nitmto and sulphuric acid, which produce the fumes of nitric 

 acid ; at the other end is a boiler in which large quantities of 

 steam are generated, and ejected into the chamber by means of 

 pipes. There is an opening at F to admit air and produce a 

 current through the chamber ; sometimes, thoroughly to mix the 

 various vapours, several partitions divide the chamber, having 

 their openings alternately at the top and near the floor. The 

 SO, as soon as formed fails and combines with the water ; this 

 process generally proceeds until the acid reaches a density of j 

 1'50. This is removed from the chamber and boiled in shallow | 

 leaden pans; when it reaches a density of 1'750 it corrodes the j 

 load, and therefore a further condensation is carried on in pla- 

 tinum vessels. The oil of vitriol of commerce is generally impure, 

 containing lead sulphate, as well as sulphates of any bases, lime, 

 tc., which the water may contain, and if the acid has been 

 made from iron pyrites, which is the Ciise with all English acid, 

 it is sure to contain arsenic. To decide if this be the case, 

 develop hydrogen with the acid, ignite it, and the flame will 



bo bluish (March's tost). One of the oxides of nitrogen u 

 generally present thU may be ascertained by the tent given for 

 nitric acid. 

 The presence of other salts may be determined by evapo- 



Fig. 47. 



rating some of the acid in a platinum crucible ; if any be pre- 

 sent, they will remain. 



Properties. This acid forms sulphates. It ha* a great 

 affinity for water, of w'lich it can take np fifteen times its 

 weight if exposed long enough to the atmosphere. In com- 

 bining with water, the temperature is greatly increased, and the 

 volume of the mixed liquids is less than the sum of their 

 volumes. The maximum condensation, 3 per cent., ia reached 

 when 3 volumes of acid are mixed with 2 of water. The 

 best test for sulphuric acid is barytic water, or a chloride or 

 nitrate of barium ; the barium displaces any other base from 

 its combination with the acid, and forms the insoluble barium 

 sulphate, which falls in a white powder ; thus 



H,SO. + BaO = H,O + BaSO. 



The remaining five oxides of sulphur are not of sufficient 

 interest to require a notice here. 



COMPOUNDS OF SULPHUR AND HYDBOOBH. 



Sulphuretted Hydrogen, or Hydric Sul2)hide (Symbol, H t S; com- 

 bining weight, 34; density, 17). This gas is always procured 

 by treating some metallic sulphide with sulphuric acid. The 

 sulphide of iron may be conveniently made by heating a rod 

 of iron, such as that from which nails are made, to a strong red 

 heat, then touching it with a stick of brimstone; the sulphur 

 and the iron combine, forming ferric sulphide, FeS. In the 

 same bottle in which hydrogen or carbonic acid gas was made, 

 place this sulphide, and add diluted sulphuric acid 



FeS + H a SO. = FeSO. -f H, S ; 



that is, iron sulphate (green vitriol) and sulphuretted hydrogen 

 are the results of the reaction. 



Properties. It is this gas which imparts to rotten eggs their 

 offensive odour. In the decomposition of the albumen, the sul- 

 phur which it contains unites with the hydrogen another of its 

 constituents producing the gas. When passed through a red- 

 hot tube, it is decomposed into sulphur and hydrogen ; the 

 latter having a volume equal to that of the undecomposed gas, 

 as this equation would indicate : 



H S S = H, + S 



2=2. 



The gas is very poisonous, but when largely diluted with air, it 

 acts as a very powerful narcotic. 



It burns with a feebly luminous flame into water and sulphu- 

 rous acid, a quantity of sulphur being deposited in the jar from 

 incomplete combustion. Water, at ordinary temperatures, ab- 

 sorbs three volumes of the gas, and in this manner it may be 

 kept for laboratory purposes ; only oxygen must be exclnded, 

 for otherwise the hydrogen will be separated to form water, 

 and the sulphur be deposited. This solution reddens litmus, 

 and is therefore sometimes called hydro-sulphuric acid ; when- 

 over an oxide of a metal is presented to it, the metal becomes a 

 sulphide, and the hydrogen of the gas with the oxygen forma 

 water, thus : 



CuO + H,8 = CuS 4- H,O. 



From the variety of colours which sulphides exhibit, and their 

 behaviour under certain circumstances, this gas becomes a valu- 

 able test agent. By consulting the following table the teats 



