ELEMENTARY BODIED] 



CHEMISTRY. 



311 



This is a very delicate operation, because so many cir- 

 cumstances interfere with the accuracy of the result. 

 When the atmosphere is at a high temperature, it con- 

 tains a large amount of moisture, and so vitiates the 

 calculations which have to be obtained, unless due allow- 

 ance be subsequently made. The same remarks apply to 

 temperatures below that of 60, which Is the usual 

 standard ; because, in that case, the absence of mois- 

 ture in the air below 60, would also give false results. 

 The gases are, therefore, carefully dried by passing them 

 through a tube containing chloride of calcium, or 

 through strong sulphuric acid, either of which has so 

 great an attraction for aqueous vapour as to abstract 

 It readily. 



The weight of the exhausted flask, deducted from that 

 obtained when the vessel is full of air, gives the weight 

 of the air which the flask would contain. The gas which 

 is to be weighed, after having been dried, is then passed 

 into the flask, which should be again exhausted, and 

 subsequently refilled with the gas. By these means 

 any chance of admixture with air left in the flask by 

 the first exhaustion is avoided. Great care, howevei, 

 must be taken that the gas is in a perfectly pure state, 

 otherwise its accurate specific gravity cannot be obtained. 

 An allowance must be made, in the subsequent calcu- 

 lation, for the expansion or contraction of the gas, if its 

 temperature be either above or below 60. The neces- 

 sary data for this purpose have already been given.* 

 The flxsk, thus filled with gas, is then carefully weighed, 

 and if its capacity be exactly 100 cubic inches, the ratio 

 of its .veight to that of 100 cubic inches of air will at 

 once be found. If the flask be of greater or smaller 

 capacity, its reduction to that of 100 cubic inches, or the 

 ratio of the weight of air to that of any gas, and, there- 

 fore, its specific gravity, is simply an ordinary arith- 

 metical question. 



We must, however, add another element of inter- 

 ference with respect to the accuracy of the results thus 

 obtained. It is that of atmospheric pressure, which 

 may be entirely neglected in solids, and in most cases in 

 liquids As the atmospheric pressure lessens, all gases 

 proportionally expand ; and as it increases, gases con- 

 tract in bulk. Now the usual standard of the specific 



gravity of gases is dry air, at a temperature of 60, and, 

 under a mean pressure, equal to that which supports 

 30 inches of mercury in the barometric column. Any 

 excess or deficiency of pressure is allowed for, and 

 proper corrections are made. The subject has already 

 been referred to ; ) and we shall not extend our remarks 

 thereon. 



The student will do well to repeatedly practise himself 

 in taking the specific gravities of solids and liquids. 

 With respect to gases, we may observe, that he caunot 

 hope to obtain anything like accurate results until he is 

 well used to experimental manipulation. If, however, 

 he possess the necessary apparatus, he can try the 

 weight of different gases, comparing them with that of 

 the air : and for such purposes, it may be useful if we 

 state, that dry air, at 60 Fah., and 30 inches barometric 

 column, weighs 31 '0117 grains for each 100 cubic inches. 

 There are certain phenomena observed in some com- 

 pounds, which are partly the result of physical and che- 

 mical actions, such as those of isomorphism, isomerism, 

 and dimorphism. By the term isomorphism, we mean 

 that bodies may have similar external forms, such as 

 crystals, itc., and yet have entirely different chemical 

 constitution. Isomeric bodies have similar chemical 

 constituents in the same proportions, and yet their ex- 

 ternal form may differ, as in sugar and starch. Some 

 bodies have two different forms, or one dimorphic, 

 under different circumstances. Thus phosphorus has a 

 rich yellow, and partly crystalline appearance at ordinary 

 temperature ; but if it be considerably heated, it loses 

 all external regularity of structure, and becomes a 

 shapeless red mass. These varieties of form, doubtless, 

 depend on a peculiar arrangement of the atoms of a body, 

 produced by the action of two or more forces. We shall 

 leave a fuller consideration of these subjects to the next 

 chapter, when we shall meet with numerous instances 

 which will fully illustrate these peculiarities. 



In the following page will be found a table of the 

 elements, their symbols, equivalents, (to. ; to which the 

 attention of our readers is especially directed, as form- 

 ing the basis of all the calculations involved in chemical 

 science, and to which we have already referred in our 

 previous pages. 



CHAPTER II. 

 THE CHEMICAL CHARACTERS OF THE ELEMENTS, AND THEIR COMPOUNDS. 



HAVING reviewed the various agencies and circum- 

 stances which govern chemical phenomena in every 

 species of matter, we shall now proceed to describe the 

 elementary bodies, and the compounds to which their 

 union gives rise. We have already remarked that almost 

 every writer on chemical science adopts a different arrange- 

 ment in treating the subject ; and we shall, therefore, not 

 hesitate to adopt a similar course, more especially as our 

 previous pages have contained ample remarks and ex- 

 periments on subjects which ordinarily form the intro- 

 ductory matter of chemical treatises. For these, we 

 refer our readers to the sections on Heat, Light, Elec- 

 tricity, and Magnetism ; to which we shall frequently 

 allude, and the subjects of which we shall presume that 

 the student has become fully acquainted with. 



We shall commence this portion of the subject by 

 describing the properties of such of the elements as, by 

 combining with others as bases, produce definite chemical 

 compounds. Of these, are Oxygen, Chlorine, Iodine, 

 Bromine, and Fluorine. 



We shall next take up Hydrogen and Nitrogen, which 

 will bo succeeded by another group, including Carbon, 

 Sulphur, Phosphorus, &c. The metallic elements will 

 then be dealt with ; and we shall divide these into tlireo 

 classes ; namely, Alkaligeneous, Calcigeneous, and Metals 

 proper. The combinations of Oxygen, Chlorine, <fcc., 

 will be considered in connection with each metallic 

 See ante Sfctitm 1, "Heat." 



element ; and the salts produced by the combination of 

 such bases with acids, will be ranged under the description 

 of the base itself. 



By this plan, we hope first to give a general idea of 

 those substances which, by their general action, have the 

 power of making numerous and analogous compounds ; 

 and afterwards we shall deal with those bodies which 

 act as bases to the former, and so either become the 

 subjects of synthesis or analysis. 



In this chapter we shall principally confine our attention 

 to inorganic substances, or those in which vital action is 

 not present. We shall, however, touch incidentally on 

 many organic coirpouuds, or those with which vital action 

 is connected. In the following chapter, we shall chiefly 

 deal with whit ha^ been called Organic Chemistry ; and 

 in those which succeed it, we shall take up the subjects 

 of Analysis, Agricultural Chemistry, and the general 

 applications of Chemistry to Arts and Manufactures. 



Many of our future remarks will be almost unintelligible 

 to the student, unless he have become acquainted with all 

 the subjects which have already been treated on. As we 

 have remarked in the various preceding sections, each 

 has a direct connection with the other. This arrangement 

 prevents needless repetition, and saves the time and 

 trouble of both reader and writer. At the present time, 

 each branch of science is so linked with others, as to 

 make it impossible to separate them. 



t See ante Section 1, " Heat* 



