Page:The American Cyclopædia (1879) Volume VI.djvu/713

CHEMICAL EQUIVALENT 701 tiads, and vice versa. the unit : Hydrogen is adopted as EQUIV 4XENTS. Old. New. Al. 18-7 27'4 Sb 122 122 As 75 75 Ba. 68-5 187 Bi 210 210 B 11 11 Br. 80 80 Cadmium Cd. 56 112 6's 133 133 Calcium Ca. 20 40 Carbon C. 6 12 Ce 45'7 91-4 Chlorine .... Cl 35-5 85-5 Chromium Cr. 26-1 52-2 Cobalt Co 80 60 Cb 94 94 Copper .... Cu 81'7 63-4 Didymium D. 47-5 95 Erbium E. F 56-3 19 112-6 19 Glucinum Gl. 4*6 9-2 Gold Au. 197 197 II 1 1 Indium. . In 56-7 113-4 Iodine /. 127 127 Iridium Ir. 99 198 Fe 28 56 Lanthanum La. 46 92 Lead Lithium Pb. Li 103-5 7 207 1 Magnesium. Me 12 24 Manganese Mn 27-5 55 Mercury .... He. 100 200 Molybdenum Mo. 48 96 Nickel Ni 29 58 Nitrogen N. 14 14 Osmium Os. 100 200 o 8 16 Palladium . . . Pd. 53 106 Phosphorus p. 31 31 Pt 98'7 197-4 Potassium 89-1 39-1 Rhodium Ro 52 104 Rubidium Bb. 85-4 85-4 Ruthenium Ru 52 104 Selenium Silicon Se. Si 39-5 14 79 28 Silver Aa 108 108 Na 23 23 Strontium Sr 44 88 Sulphur s 16 32 Tantalum Ta. 182 182 Tellurium Te 64 123 Terbium Tb. 87-7 75-4 Thallium Tl. 204 204 Thorium Th 59-2 118-4 Tin 8n. 59 118 Titanium Ti 25 50 Tungsten W. 92 184 Uranium 60 120 Vanadium v. 51-3 51-3 Yttrium Y. 30-8 61-6 Zinc Zn 82-5 65 Zirconium Zr. 44-8 89-6 Each element has its own special combining equivalent, and is incapable of uniting with other elements except in this proportion or some multiple of it. The equivalents of com- pound bodies are represented by the sums of the equivalent numbers of all the elements which enter into their composition. The weights of the equivalents of the _ elements are ascertained by determining experimentally how much of each is required to replace the others in their combinations with some well known element, the weight of the equivalent of which has been assumed. Thus, the quan- tity by weight of each element which unites with one equivalent of oxygen to form a pro- toxide, analogous to water, is usually consid- ered to represent its equivalent. A knowl- edge of the exact weights of the equivalents is of the first importance to chemists ; all calcu- lations regarding the composition of bodies, as in analysis, or of the quantities of materials to be employed in the manufacture of com- pounds, being based upon them. As the equiv- alent numbers express nothing but the relative weights in which the elements unite with each other, it is evident that the weight of any one equivalent may be arbitrarily chosen as a stan- dard to which all the others shall be referred ; it is essential only that the relation be strictly observed. Tables of equivalents are thus con- structed, in which the equivalent weight of each of the elements is attached to its name. Several standards have been selected, but only two have ever been generally used. The equivalent weight of hydrogen, being smaller than that of any other element, was regarded as unity by Dalton, who referred all the other equivalents to it. This system has been gen- erally adopted by the chemists of Great Britain and the United States. It possesses the very great advantage that in it the equiyalents are represented by small numbers, many of them without fractions, which are convenient in calculations, and can be easily retained by the memory. Another table, in which the equiv- alent weight of oxygen is assumed to be 100, has been much used on the continent of Eu- rope. It was proposed by Berzelius, mainly it would seem for the purpose of discounte- nancing a theory advanced by Prout, that all the equivalent numbers are simple multiples of that of hydrogen ; superiority was claimed for it on the ground that as oxygen is the most abundant of all the elements, and as the greater number of bodies studied by chemists are com- pounds of it, calculations would be simplified if its equivalents were regarded as equal to 100 ; in which case it is only necessary to add 100, 200, 300, &c., to the equivalent weight of the element with which oxygen is combined, in order to ascertain the equivalent weights of its several oxides. The equivalent of sulphur, a very common element, would also have a simple expression, being equal to 200. But these instances do not at all compensate for the high numbers by which the other equiv- alents must be represented; numbers which cannot be remembered without great difficulty, and which render even the most common cal- culations extremely laborious unless logarithms are resorted to. Berzelius, who believed that the equivalent numbers should be regarded as entirely accidental and unconnected with each other, desiring to give them the most accurate expression possible, introduced the custom of attaching to them large decimal fractions ; indeed, the power to do this which is afforded by the high numbers of his system has always been claimed as one of its advantages. The