rni:.MisTKV. 



kept, entirely unchanged, for uiauy year*. Wo havo 

 lively mentioned that voltaic batteries, and electro- 

 UKjUllurgioal processm, require certain temperatures for 

 tliuir successful working.* In many iiuUiuco, how- 



, the ohwnut avaiU himself of extreme cold tu 

 maintain the exuteoeo of many substances; an U the 

 cue with clil.iriilo of nitrogen, peroxide of hydrogen, 

 and other compound*. In those there i* a continual 

 tendency toward* decomposition if a low temperature be 



iiiuuUinod ; and heuoo the employment of the meant 

 nan. 



The rapidity with which chemical action ensues be- 

 tween bodies, d|>ends on tlio intensity of attraction 

 they hare for each otln-r. Thus, if nitric acid be poured 

 on silver or copper, the action is most violent ; whereas 

 i. -no is peroaivod ou platina. If, again, the acid be 

 diluted with water, the intensity of its action is di- 

 minished, for fewer particle* of the metal and acid 



in contact. In some cases, a sudden suspension 

 of action take* place : thus, nitric acid will act violently 

 KII the metal mm, and then all chemical action will 

 ease, the iron having assumed a passive state. At 

 times, the attraction is so powerfully exerted as to 

 pi.l iico a large amount of heat and light as when 

 sulphuric acid is poured on chlorate of potass and sugar; 

 at other times, intense cold is produced as when freezing 

 mixtures are dissolved in water. Indeed, it would be 

 Lni|nnil>le for us to sum up the great variety of instances 

 in which the exercise of chemical attraction is mani- 

 fested, or to enumerate the peculiar effect which it pro- 

 duces. These, however, we shall frequently notice in 

 our future progress our desire having boon just to 

 put the Ktudent in possession of leading facts, which 

 may servo as a guide, to further details. 



vrAUY BODII.S. AND THEIR COM- 

 UIMN<; rilol'OKTloXJs UK EQUIVALENTS. 



T.I pic-, cut any complication of subjects, in our previous 

 remarks we have avoided any mention of elementary 

 substances, and the proportions in which they unite 

 together. These matters must now form the subject of 

 our imr-ii-ations. 



All substances which have hitherto resisted our utmost 



in to procure others from them of a different 



cluu-actcr or quality to themselves, have been termed 



elementary; and the number ha* been largely increased 



during the present century. For this wo are largely 



indebted to the researches of Sir Humphry Davy, who, 



l>v ai'l of (lie \ ry, was enabled to decompose 



.dkalica potass and soda, and some of the earths. 



Since his time, other discoveries have boeu made, es- 



l<ccially in connection with metallic l>< 



In iiuwt chemical works these bodies are arranged in 

 groups; but, unfortunately, this arrangement is either 

 modified or altered by each authority on the subject. 

 The dilliculty of obtaining a settled plan in this respect, 

 lies in the fact, that the constant accessions which are 

 obtained to chemical wcicnec, invalidate many of the 

 i -i which had lioen previously made. The 

 jioint, however, U ii"t of . xtivme importance; for as 

 each element ILLS its own distinctive character, it follows 

 that tlie OOmpOWldl it forms never exactly resemble 

 those of other clement*, although a great analogy may 

 exist between them. \Vu take hydrogen as an instance 

 of the kind; for, in many of its chemical relationships, 

 it U-havi-s precisely like a until; i:.-l yet, considering 

 iu physical characters, it seems the farthest rcni<.\.'d 

 of any from that clans of i un. ammonia, 



which is known to be a compound milwtanco, present*, 

 under certain cir.-umitiuices, every indication of nn-tallic 



chani'-t.-r; and, in I I, the existence of ammonium is 



theoretically admitted at the present day : yet no 

 sn.-ilogy exUU between it and the metals in tin- cha- 

 racters which, of all others. !i them from 

 other an butanoes. Our present ixwition, in these respect*, 

 U, therefore, one of great doubt and ] for, 

 whiUt we see distant glimmerings of new facts by their 



SM mmlt, p. 110. 



analogies, the rigid system of philosophy/ cannot allow us 

 to jump at C". ..i true, but ar. 



capable of present pn-.f. In our future pages, u .-.lull 



f<iro use the license which tin : of iloulit 



l>enuiU ; and after dealing with g"iieral principles, shall 



d to give the natural history of each of thu 

 elen.. i" the compound ;. from them. 



To Dr. Dalton, of Manchester, we owe the disc<>. 

 that bodies combine in relative proportions ; or, in other 

 words, that every substance, elementary or compound, 

 has a numerical ratio, in which alone it will form 

 compounds with others. This ratio has had applied to 

 it the terms, "equivalent," "combining propor't 

 and "atomic weight;" but, in our future pages, we shall 

 only use that of equivalent, as expressing the fact-s of 

 the case most clearly. What U meant, is simply that 

 each substance must be taken in definite quantities 

 to form a definite compound with others. Tim-, 

 eight grains, ounces, or pounds, of oxygen, must bo 

 united with one part of hydrogen, to form nine 

 parts of water. If an excess or deficiency in these 

 quantities be employed, then only so much water will 

 lie produced as the proportion of eight of oxygen and 

 one of hydrogen would afford, and the element in 

 excess of this ratio would be left free. Again, ten 

 parts of oxygen would not unite with one of hydrogen, 

 because the ratio we have named is not maintain* >l 

 Sixteen parts, however, of oxygen, and one of hydr, , 

 may unite, because in that we have the ratio existing. 

 A compound very different to water, however, would bo 

 the result, which, of course, might be expected from the 

 union of two bodies in proportion, different to those 

 producing water. We may take another illustration in 

 the case of oil of vitriol, or, as it is chemically ten 

 sulphuric acid. This is composed of three parts of 



a, and one part of sulphur, if it be entirely free 

 from water. In its commercial state, when pure, it is 

 always combined with one part of water. Xow the 

 equivalent of sulphuric acid is obtained by adding 

 together that of its constituents, thus : 

 Quantity of each material. Equivalent of each. 



1 part of sulphur 1C 



3 parts of oxygen 8 



1 part of water, composed of 1 

 oxygen, 8: 1 part of water, v 9 

 composed of hydrogen, 1 . J 



ToUU 



. 10 



. -1 



Equivalent of sulphuric acid = 49 



Or, in other words, we may say, that one equivalent 

 of sulphur, three of oxygen, and one of water, t'orm one 

 equivalent of sulphuric acid, which, with reference to 

 other compounds, lias an amount equal to T.I. 



\\'e will now take an instance iu which both sulphuric 

 acid and water are united with a metal which, how. 

 has first combined with oxygen, and so formed what is 

 called an oxide ; and for this purpose we will choose the 

 green copperas, or sulphate of iron. Oxide of iron is 

 that metal united, iu this case, with one equivalent of 

 ti ; and as the equivalent of iron is L'S, it follows 

 that the equivalent of its oxide will be 'M. Now this 

 salt of iron is composed of one part of oxide, one of 

 sulphuric acid, and seven of water; and its equivalent, 

 will bo as follows : 



Quantity. Kquiralcnt. 



1 of oxide of iron 'M . . . 



1 of sulphuric acid, free from 1 , n 



water / 



7 of water ....... 9 ... 



Eq.iivaient of itulphate of iron : 



These throe instance* of water, sulphuric acid, and 

 sulphate of iron, will illustrate the mde in which the 

 equivalents of compounds are formed. The last shorts 



how that of two i ipoiinds, united together, is obtained. 



If the student fully comprehend tin , will have 



got over all difficulties presented in the study of the 

 numerical value of equivalents ; and have luado a 



