KQUIVALENTS.] 



CHEMISTRY. 



303 



advance in the study of chemical science. In the case of 

 organic compounds, precisely the same plan is adopted ; 

 but as they present theoretical difficulties, we shall not 

 enter into their discussion for the present. 



It will be asked, however, how these equivalents are 

 found, with respect to the elementary bodies ; 7id 

 although the practical part of the question is one re- 

 quiring the greatest skill and experience, its explanation 

 will not be difficult. If, as we have shown, every body 

 lias a definite combining proportion it follows, whenever 

 we examine it, we shall procure its constituents in their 

 proper proportion of combination. For instance, if we 

 decompose water by any means, we always obtain one 

 part of hydrogen gas from nine of water, provided the 

 operation has been completely performed : we there'- 

 fore infer the presence of eight parts of oxygen. Or, if 

 we prefer to take the oxygen, and weigh it, in com- 

 bination, say with iron, we find that, if pure iron 

 had been used to the extent of 28 grains, it would 

 weigh, after the operation, 36 grains, from which 

 we should infer that eight grains of oxygen had been 

 added to it. But even during the process of finding 

 the equivalent of oxygen, we gain that of the iron ; for, 

 supposing we used 50 grains of pure iron in de- 

 composing nine grains of water, wo should find that 

 tlie iron only weighed 58 grains at the end of the 

 experiment; and as we could, by means we need not 

 separate the iron which had. from that which 

 had not been oxidised, we should di-ec P \er, that out 

 of the 68 grains, there would be 22 which had 

 eacaped oxidation. This number deducted from 58, 

 i.u. ! ]<-i\c :>i> as the equivalent of oxide of iron; 

 and subtracting eight, the equivalent of oxygen, we 

 should obtain 28 as the equivalent of iron. This 

 mode of findi.ig metallic equivalents is not that prac- 

 tically adopted in all cases; but we have availed our- 

 selves of it because it exhibits the facts with which 

 we are dealing. We can, however, illustrate the method 

 of finding equivalents by another process, which is that 

 of decomposition ; and this is the plan almost alwsiys 

 adopted ; and one which our readers can roughly try for 

 themselves, after the following manner. Of course they 

 must not expect to obtain anything like accurate results; 

 for it requires great care and readiness of manipulation 

 to succeed in such delicate investigations. 



riment 4. Dissolve 110 grains of jnire silver 

 (ordinary coin will not do) in some dilute nitric acid ; 

 and when the whole is in solution, add common salt, 

 also dissolved in water, until no more white powder 

 falls down to the bottom of the vessel. Whim this has 

 settled, pour away the water, and add fresh until the 

 last washing does not in the least taste of salt, inking 

 great care that not a particle of the white powder is 

 lost. Then pour the whole of the powder on to a 

 piece of white blotting-paper so as to filter it, taking 

 the precaution of weighing the paper accurately before- 

 hand. The whole is then to be carefully dried, and, 

 whilst still warm, must be weighed. It will be found, 

 that the powder, after deducting the weight of the paper, 

 will weigh about 144 grains, of which 36 parts are chlo- 

 rine, leaving 108 parts of pure silver as the remaining 

 constituent of the powder. Thus, knowing the equiva- 

 lent of chlorine, we infer that of silver to be 108. 



These results are controlled by experiments with other 

 combinations of the same body ; and, by pursuing a 

 similar course, the equivalents of any element may be 

 ascertained. The numerous precautions which have to 

 be observed, and the difficulty of obtaining the sub- 

 stances in a state of sufficient purity, together with 

 other circumstances into which we shall not enter, 

 render the attempts to obtain exact and reliable results 

 one of the most difficult operation* in experimental 

 science. We hence find, that tables of equivalents, 

 compiled by different experimenters, vary somewhat in 

 the numbers given to each element. 



Of course some standard is required to commence 

 with, the multiples of which shall form the equivalents 

 of all other bodies. Hydrogen has been chosen, and 

 adopted, by nearly every English chemist; ami if no 



other be named in chemical works, the reader may 

 always assume such to be employed. Some have pro- 

 posed oxygen as the unit, from the importance of its 

 combinations ; but such do not compensate for many of 

 the advantages of the hydrogen scale. Hydrogen is the 

 lightest body in nature, and has the lowest combining 

 proportion. There is, however, one difficulty which 

 presents itself ; and it is, that although hydrogen and 

 oxygen combine in the proportion of one to tight l>y 

 /, they do in that of two to one by measure. This, 

 however, only affects the gases ; but a late writer has 

 proposed to double the equivalent of oxygen, so as to 

 meet the difficulty. It is improbable that such a pro- 

 position will be generally adopted. 



CHEMICAL MANIPULATION AND APPARATUS. 



As we shall suggest a large number of experiments in 

 future pages, with the intention that our readers may 

 become practically acquainted with chemistry, it will 

 be advisable that we should give some description of the 

 apparatus which will be required, and the best mode oi 

 using and managing it. We shall, as far as possible, 

 study the means of our readers ; and therefore surest 

 the most economical and effective mode of carrying out 

 the experiments. Many persons have an idea that the 

 study of chemistry is a veiy expensive one. Such is 

 not the case ; for all the leading class experiments, teach- 

 ing the elements of the science, may be performed with 

 apparatus not costing more than ten shillings; and thfa 

 chemicals are exceedingly cheap. If, however, the 

 student enter into an extended course of original re- 

 search, and the applications of chemistry to the arts 

 and manufactures, and become, as many persons do, 

 enamoured of the study, we should certainly decline to 

 mention the extent of means required ; for any amount 

 of money may be so exj>ended. 



Much of the success which may be obtained in expe- 

 rimenting, depends on neatness, care, and cleanliness. 

 A man may become an expert chemist, and yet may be 

 but a p<x>r philosopher ; for it frequently happens, that 

 whilst the experimenter may make the most valuable 

 discoveries of facts, he has not the mental power of 

 generalisation. On the other hand, a highly cultivated 

 mind will avail itself of these facts, and so generate 

 theories which shall embrace a multitude of effects. 

 Some persons combine both these qualifications ; yet 

 such are rare accoinplishments. But let none of our 

 readers be discouraged by these statements. " t-luum 

 ne" is a motto which may be safely adopted in 

 philosophy as in other matters'; and during the last few 

 years, the boundaries of science have been so extended, 

 as to render subdivision of labour a question not of 

 choice, but of absolute necessity. A schoolboy of our 

 time, knows more of natural philosophy, so far as facts 

 are concerned, than did all the philosophers of the days 

 of Newton and his compeers ; and the philosophers of our 

 day are but the schoolboys of those who shall succeed 

 them. 



As we shall commence with the history of the gases, 

 the various apparatus required for manipulating with 

 them will first claim our attention. 



Gases, such as oxygen, require the application of heat 

 for their production ; and, generally speaking, retorts, 

 test-tubes, or flasks are employed for that purpose. Th*; 

 following engravings illustrate Fi?. l. 



the appeararce of each of these. 

 Fig. 1 is a retort, in the bulb of 

 which the materials to be heated 

 are placed. They are made of 

 various sizes. The student may 

 provide himself with a few, varying from one ounce tc n 

 pint capacity. They require heating gently at first, tc 

 prevent the danger of cracking them. They should 

 never be cleaned until quite cold, and are then to be 

 placed stem downwards, so that the water employed for 

 that purpose may drain off, and leave the inside quite 

 dry. 

 I A good substitute for a retort, when small quantities 



