SALTS 583 sulphate of zinc, ZnS04, the metal is regarded as an electro-positive basyle, while the body SO* is regarded as an electro-negative radical, composed of the anhydride of the acid plus oxy- gen, and called generically an oxion. When the oxygen is united to sulphur, as in sulphuric acid, the oxion is specifically called a sulphion, or sometimes an oxysulphion. In the case of sulphurous acid, instead of being a sulphion it is' a sulphosion. When the radical contains nitrogen instead of sulphur, it is an oxion, which is specifically called a nitrion or a nitro- sion, according as it is a constituent of nitric or nitrous acid. The objections to the binary hypothesis are, that none of the compound radicals or oxions, SO 4 , N0 3 , or CO S , have ever been isolated ; and it also appears im- probable that a. compound which is held to- gether by such powerful attractions as in pot- ash exist between potassium, the most highly electro-positive, and oxygen, the most highly electro-negative element, should be decom- posed by the action of carbonic anhydride, COa, parting with its oxygen, so that K 2 O + COa should become K a ,CO s instead of K a O,CO a . Chemists are now more inclined to regard a salt, when once formed, as a whole, and not as consisting of two distinct parts, although it is probable that during the act of combining the electro-chemical relations of the constit- uents are distinct and opposite. It is some- times convenient, however, to regard salts as having the constitution of binary compounds, and as consisting of a basyle and a radical con- stantly held together by opposite electric po- larities. It was formerly supposed that salts are formed only between acids and bases of the same class ; that is, that both members must be oxides, sulphides, chlorides, &c. ; and this was consistent with the ternary hypothe- sis, which regarded the salt as a combination of a compound base with an anhydride and not with its radical, as has been above illustrated. Upon this hypothesis it will be seen that sul- phuret of potassium could not form a salt with sulphuric acid. It required decomposition to effect this, including the evolution of sul- phuretted hydrogen gas, thus: K a S + H a SO 4 = K a SO 4 + H a S. But according to the binary theory a similar reaction takes place on the addition of sulphuric acid to oxide of potas- sium, water instead of sulphuretted hydrogen being formed : K a O + H 2 SO 4 =K a SO 4 + H a O. There are three varieties of salts which de- pend upon the relative proportions of radical to basyle, or, in common language, of acid to base. They are called neutral or normal, acid, and basic or subsalts. 1. Neutral Salts, A salt is commonly said to be neutral when the characteristics of both acid and base have neutralized each other, and this condition is usually regarded as existing when the salt has neither the effects of acids nor alkalies upon certain vegetable colors. The blue color of litmus is changed to red by an acid, and again restored by an alkali, while a perfectly neutral salt produces neither of these effects. The yellow of turmeric is turned brown by an alkali, and is restored by an acid. But there are some salts which are regarded as neutral in composition, or, to use a more appropriate term, normal, which have the power of chang- ing vegetable blues to red, and vice versa. There are some acids (and they are all now re- garded as salts of hydrogen) that contain only one atom of hydrogen which can be displaced by one atom of a monad metal. Such acids are said to be monobasic, and among them are hydrochloric, HC1, nitric, HNO$, and acetic, HCaHsOa. When these acids unite with bases, they are capable of forming only monobasic salts, that is, salts containing one atom of ba- syle. Other acids contain two atoms of hydro- gen, which may be replaced by two atoms of a monad metal like potassium, or one equiva- lent of a dyad like zinc. These acids are called dibasic, and among them are sulphuric, JIsS0 4 , and tartaric, H a C 4 H 4 0. Other acids again contain three atoms of hydrogen, which may be replaced by three atoms of a monad metal, or one atom of a triad ; and such acids are said to be tribasic, of which tribasic phospho- ric acid, H 3 PO B , and citric acid, HsCgHeOT, are examples. Acids and salts which contain more than one equivalent of basyle are said to be polybasic. In general it may be said that when all the atoms in the hydrogen basyle of the acid are, in the formation of the salt, replaced by an equivalent number of atoms of the metallic basyle, the salt as formed will be normal, or, in common language, neutral ; although it must be remembered that some normal salts will change vegetable colors. 2. Acid Salts. When the atoms of the hydrogen basyle are only partially replaced by a metal- lic basyle, the salt so formed is an acid salt, the acid character of the hydrogen compound (acid or salt) not having been neutralized by an equivalent of metallic basyle. The formation of a true acid salt therefore requires a poly- basic acid, for if the one basyle of hydrogen in an acid is replaced by one metallic basyle, the salt so formed will be normal. An exam- ple of an acid salt is bisulphate of potassium (hydric-potassic sulphate), KHS0 4 , where only half of the basyle hydrogen is displaced, and there is only one atom of potassium instead of the two which are required to replace the hydrogen in sulphuric acid, H S SO 4 . Other examples are the organic salts, bitartrate of potassium (cream of tartar, hydric-potassic tartrate), KHC 4 H 4 O, and bicarbonate of po- tassium (hydric-potassic carbonate), KHCO. The normal salts corresponding to these are : potassic sulphate, K a SO 4 ; potassic tartrate, K 9 C 4 H 4 ; and potassic carbonate, K a COa. 3. Basic Salts. These are such as contain a greater number of atoms of metallic basyle than there were atoms of hydrogen basyle in the acid. An example of such salts is basic mercu- ric sulphate (turpeth mineral), HgSO 4 ,2HgO, which contains three atoms of mercury in
