82 



EQUIVALENTS. 



composition of the salts affords an excellent illus- 

 tration of this subject ; and, to exemplify it still 

 further, a list of the proportional numbers of a few 

 acids and alkaline bases is subjoined. 



Fluoric acid, . . 10 Lithia, 

 Phosphoric acid, . US Magnesia, 

 Muriatic acid, 

 Sulphuric acid, 

 Nitric acid, 

 Arsenic acid, . 



37 Lime, 

 40 Soda, 

 54 Potash, . 

 62 Strontia, . 

 Barytes, 



18 

 20 

 28 

 32 

 48 

 82 

 78 



Now, bodies uniting according to their proportional 

 numbers, as has been seen above, the proportion of 

 each base expresses the precise quantity required to 

 neutralize a proportion of each of the acids. Thus 

 eighteen of lithia, thirty-two of soda, and seventy- 

 eight of barytes combine with ten of fluoric acid, 

 forming the neutral fluates of lithia, soda, and barytes, 

 and are termed equivalents of each other, as well as 

 of fluoric acid. The same fact is obvious, with 

 respect to the acids ; for twenty-eight of phosphoric, 

 forty of sulphuric, and sixty-two of arsenic acid unite 

 with twenty-eight of lime, forming a neutral phos- 

 phate, sulphate, and arseniate of lime, and these 

 acids, in like manner, are equivalents of each other 

 and of lime. These circumstances afford a ready 

 explanation of the fact, that when two neutral salts 

 mutually decompose one another, the resulting com- 

 pounds are likewise neutral. If eighty-eight parts of 

 neutral sulphate of potash are mixed with 132 of the 

 nitrate of barytes, the seventy-eight barytes unite 

 with the forty sulphuric acid, and the fifty-four nitric 

 acid of the nitrate combine with the forty-eight 

 potash of the sulphate not a particle of acid or 

 alkali remaining in an uncombined condition. 



The method of determining the proportional num- 

 bers, as might be anticipated from what has gone 

 before, is, to analyze a definite compound of two 

 simple substances which possess an extensive range 

 of affinity. No two bodies are better adapted for 

 this purpose than oxygen and hydrogen, and that 

 compound of these is selected which contains the 

 smallest quantity of oxygen. Water is such a sub- 

 stance ; and it is therefore regarded as a compound 

 of one proportion of oxygen to one proportion of 

 hydrogen. But analysis proves that it is composed 

 of eight parts of the former to one of the latter, by 

 which the relative weights of their proportions are 

 determined, that of oxygen being eight times heavier 

 than that of hydrogen. Some compounds are next 

 examined which contain the smallest proportion of 

 oxygen or hydrogen in combination with some other 

 substance, the quantities of each being the smallest 

 that can unite together. Carbonic oxide with 

 respect to carbon, and sulphureted hydrogen with 

 respect to sulphur, answer this description perfectly. 

 The former consists of eight oxygen and six carbon ; 

 the latter of one hydrogen and sixteen sulphur. The 

 proportional number of carbon is, consequently, six, 

 and of sulphur, sixteen. The proportions of all 

 other bodies may be determined in the same manner. 

 Since the proportional numbers merely express the 

 relative quantities of different substances which 

 combine together, it is, in itself, immaterial what 

 figures are employed to express them. The only 

 essential point is, that the relation should be strictly 

 observed. 1'hus we may make the combining pro- 

 portion of hydrogen 10 ; but then oxygen must 

 be 80, carbon 60, and sulphur 160. Doctor Thom- 

 son makes oxygen I, so that hydrogen is eight times 

 less than unity, or 0.125, carbon 0.75, and sulphur 2. 

 Doctor Wollaston fixes oxygen at 10, by which 

 hydrogen is 1 25, carbon 7.5, and so on. According 

 to Berzelius, >xygen is 100. The system of Wollas- 

 tca becomes the same as doctor Thomson's by merely 



dividing by 10 ; that is, by placing the decimal point 

 more to the left by one figure ; and then, if we 

 multiply by 8, it is converted into Mr Dalton's scale, 

 in which hydrogen is the standard. 



Tables of the combining quantities of all chemical 

 agents liave been drawn up and arranged to guide 

 tfte chemist in experimental researches. The utility 

 of these tables is very extensive. Through their aid, 

 and by remembering the proportional numbers of a 

 few elementary substances, the composition of a 

 great number of compound bodies may be calculated 

 with facility. By knowing that 6 is the combining 

 proportion of carbon, and 8 of oxygen, it is easy to 

 recollect the composition of carbonic oxide and 

 carbonic acid. the first being 6 carbon + 8 oxygen, 

 and the second 6 carbon + 16 oxygen. 40 is the 

 number of potassium, and potash, being its pro- 

 toxide, is composed of 40 potassium -f 8 oxygen. 

 From these few data, we know at once the composi- 

 tion of the carbonate and bicarbonate of potash. 

 The first is 22 carbonic acid + 48 potash; the 

 second, 44 carbonic acid + 48 potash. 



These tables are rendered still more useful, if 

 accompanied by a logometric sliding scale, the appli- 

 cation of which to this purpose was a happy inven- 

 tion of doctor Wollaston. As it is not possible to 

 include, on a single scale, the names of all substances, 

 those are selected which are the most frequent sub- 

 jects of reference. These are arranged in the order 

 of their relative weights, and at such distances from 

 each other, according to their weights, that the series 

 of numbers, placed on a sliding scale, can at plea- 

 sure be moved, so that any number expressing the 

 weight of a compound may be brought to correspond 

 with the place of that compound in the adjacent 

 column. The arrangement is then such that the 

 weight of any ingredient in its composition, of any 

 reagent to be employed, or precipitate that might be 

 obtained in its analysis, will be found opposite the 

 point at which its respective name is placed. Let 

 us illustrate its use by a few examples. 



1. The quantity of any substance, which is equiva- 

 lent to a given quantity of any other inscribed on the 

 scale, may be learned by inspection ; the quantities 

 taken being quite arbitrary, and such as are liable to 

 suit the purpose at any time. Thus, by bringing 50, 

 on the slider (in a scale where the weight of hydrogen 

 is expressed by 1), opposite to magnesia, or to its 

 equivalent, 20, it will be seen that 50 parts of that 

 earth are equivalent to 70 lime, 120 potash, &c.- 



2. It ascertains the quantity of each base that is 

 equivalent to a given quantity of any acid. Thus 

 50 on the slider being brought opposite to sulphuric 

 acid, or to its equivalent, 40, it appears thpt 50 parts 

 of this acid saturate 25 of magnesia, 35 lime, 60 

 potash, &c. In a similar manner, it is capable of 

 indicating the quantities of different acids required to 

 saturate each base ; thus 50 parts of magnesia satu- 

 rate 100 of sulphuric acid, 135 nitric acid, &c. 



3. It enables us to determine, by inspection, the 

 proportions of the components in a given quantity of 

 any substance of known composition. Thus, by 

 bringing 100, on the slider, opposite to 72, the 

 equivalent of dry sulphate of soda, we find 55.5 on 

 the slider, opposite to the equivalent of sulphuric 

 acid, and 44.5 opposite to the equivalent of soda ; 

 numbers which, together, make up 100 of the salt. 

 It expresses not only the proximate, but the ultimate 

 elements of compounds. Thus, keeping the slider 

 in the same situation as above, we find 22.4 on the 

 slider, opposite to 16, the equivalent of sulphur, and 

 33.1 opposite to 24, the equivalent of three propor- 

 tions of oxygen ; and 22.4 + 33.1 make up, together, 

 55.5 of sulphuric acid. By reference to the equiva- 

 lents of sodium and oxygen, we find also that 44 



