CHAMBERS'S INFORMATION FOR THE PEOPLE. 



When an acid and a base are mixed, a salt is 

 produced. Thus, if we gradually add a solution 

 (in water) of hydrochloric acid to a solution (in 

 water) of caustic soda, a point will be reached 

 where the mixed solution has neither the alkaline 

 reaction of the soda nor the acid reaction of the 

 hydrochloric acid. Such a solution is said to be 

 neutral, and, on examination, is found to contain 

 neither acid nor base, but a new substance, differ- 

 ent from either of them. In the case which we 

 have taken, this neutral substance is common salt. 

 A similar action takes place between every acid 

 and every base, and the fact that salts are formed 

 in this way has given rise to the nomenclature of 

 salts which was till lately in almost universal use, 

 and is still very frequently employed. This no- 

 menclature will be best explained by a series of 

 examples. Thus, 



Sulphuric Acid acts on Soda, producing Sulphate of Soda. 

 Nitric Acid H Soda, n Nitrate of Soda. 



Hydrochloric or) ~j- (Hydrochlorate or Mu- 



Muriatic Acid]" " Soda > " 1 riate of Soda. 



. Sulphuric Acid n Ammonia n Sulphate of Ammonia. 



. t . . ., (Oxide of 



Aceuc Aad 



. 



xide of) (Acetate of Oxide of 



Lead j ., \ Lat&t 



&c. &c. 



In all these cases, the name of the acid ends in -ic 

 (sulphunV, nitr/V, &c.). There are, however, acids 

 the names of which end in -ous, such as sulphurous 

 acid, nitrous acid. In such cases, 



Sulphurous Acid acts on Soda, and produces Sulphite of Soda. 

 Nitrous Acid n Potash, n Nitrite of Potash. 



And so on. 

 SulphunV Acid produces sulphate; ; Sulphurour, sulphites, &c. 



When this characteristic action of an acid upon 

 a base takes place, water is in most cases pro- 

 duced as well as the salt. This formation of 

 water is of great theoretical importance, and will 

 be adverted to again further on. 



What we have now seen enables us to define 

 acids and bases as substances opposed to one 

 another in chemical character, and capable of act- 

 ing upon one another, so that both the acid and 

 basic properties are neutralised, and salts pro- 

 duced. It is necessary, however, to note that this 

 distinction between acids and bases is one rather 

 of degree than of kind, some acids possessing the 

 acid character, and some bases possessing the 

 basic character, in a much more strongly marked 

 manner than others. Thus, some substances 

 behave as acids with strong or well-marked bases, 

 and as bases with the stronger acids ; for instance, 

 white arsenic has decidedly acid properties, and 

 forms salts with most bases, but acts like a base 

 when treated with hydrochloric or tartaric acid. 

 Alumina and green oxide of chromium are bases 

 to most acids, but acids to some of the stronger 

 bases, such as potash and lime. The salts formed 

 from a strong acid and a weak base have, gener- 

 ally speaking, when soluble, an acid reaction ; 

 those formed from a weak acid and a strong base 

 have, under similar conditions, an alkaline reac- 

 tion. Thus, sulphate of alumina has an acid 

 reaction ; carbonate of potash has an alkaline 

 reaction. 



The next point which we shall consider is the 

 relation between the quantity of acid and the 

 quantity of base required to form a salt This is 

 most easily investigated in the case of strong 

 acids and bases which form with one another 

 salts neutral to vegetable colours, although the 

 same principles apply equally to all other cases. 

 Hi 



To illustrate these principles, we shall examine 

 the relations of the acids and bases mentioned 

 above namely, sulphuric, nitric, hydrochloric, and 

 acetic acids; and the bases, caustic potash, caustic 

 soda, lime, magnesia, oxide of lead, and ammonia. 

 Let us first take a certain weighed quantity of pure 

 caustic potash (for reasons to be explained after- 

 wards, we select the quantity 56 grains*), and find 

 out how much of each of these acids is required 

 to neutralise it and form a salt. The results are 

 as follow : 



56 grains of Caustic Potash are neutralised by 



49 grains of Sulphuric Acid. 

 63 n Nitric Acid. 

 36} ii Hydrochloric Acid. 

 60 n Acetic Acid. 



These quantities 49 parts of sulphuric acid, 63 of 

 nitric acid, 36$ of hydrochloric acid, and 60 of 

 acetic acid are said to be 'equivalent' to one 

 another that is, they are equivalent as far as- 

 neutralising potash is concerned ; and these 

 numbers are called the ' equivalents ' of the acids. 

 We further find that 



49 grains of Sulphuric Acid neutralise 



56 grains of Caustic Potash. 



40 ii Caustic Soda. 



28 ti Quicklime. 



20 n Calcined Magnesia. 



in} n Oxide of Lead. 



17 ii Ammonia. 



Similarly, these quantities of the various bases are 

 said to be ' equivalent ' to one another, and these 

 numbers are called the equivalents of the bases. 

 Now, the remarkable fact in connection with these 

 numbers (the first discovered of a series of similar 

 facts, upon which the modern system of chemistry 

 is based) is, that an 'equivalent' of any acid is 

 precisely the quantity required to act upon an 

 1 equivalent 1 of any base in order to produce a salt. 

 Thus, 63 grains of nitric acid neutralise 56 grains 

 of potash, 40 of soda, and so on ; 60 grains of 

 acetic acid act upon in of oxide of lead to pro- 

 duce sugar of lead, &c. It is thus only necessary 

 to ascertain by experiment the proportion in 

 which a new base unites with one known acid, in 

 order to know in what proportion it will unite with 

 any other acid the equivalent of which is known. 



The salts thus formed are often called ' neutral 

 salts,' because, when an equivalent of a strong acid 

 acts upon an equivalent of a strong base, the 

 resulting salt has neither an acid nor an alkaline 

 reaction ; it is, however, better to call them 

 'normal salts/ because, as already mentioned, 

 such of them as have a weak acid and a strong 

 base are often alkaline, and those with a strong 

 acid and weak base are often acid in reaction 

 upon vegetable colours. They are called 'neutral' 

 or 'normal' salts, to distinguish them from two 

 classes of salts which ,we shall next, shortly, 

 advert to. If we mix 49 grains (one equivalent) 

 of sulphuric acid with water, and add 56 grains 

 (one equivalent) of caustic potash, we already 

 know that the ' normal ' sulphate of potash will be 

 produced. If, however, we add only 28 grains 



equivalent) of caustic potash, and then dry off 

 the water, we find, not, as we might expect, a 

 mixture of neutral sulphate of potash and unacted- 

 on sulphuric acid, but a salt, called the 'bisulphate 

 of potash,' or ' acid ' sulphate of potash, which has 

 been formed by the action of one equivalent of 



Instead of grains, it need scarcely be said, any other unit 

 'ounces, pounds, or tons) may be used. 



