470 FOUNDING; FOUNDRY 



Rational formula. In the above illustration we found the simplest ratio existing 

 between the elements of nitric acid. But it will be seen that, for aught that appears 

 there, it may consist of n times NO 6 . It becomes necessary, therefore, to find the 

 atomic weight of the acid, and then to find the number of atoms of the elements 

 (combined in the above ratio), which will make that atomic weight. In order to do 

 this, it will be proper to determine the atomic weight of the acid from the data pro- 

 cured by the first method, given above. In order to accomplish this, a salt was 

 analysed for the percentages of soda and nitric acid, with the annexed result : Soda, 

 36-47 ; nitric acid, 63-53. 



The required datum, namely, the atomic weight of the acid can easily be obtained 

 by saying, As the percentage of base is to the percentage of acid, so is the atomic weight 

 of the base to the atomic weight of the acid. In the instance given we have, there- 

 fore : 



36-47 : 63-53 ,:: 31 I 53-999 



Percentage of Percentage of Atomic weight of Atomic weight of 

 base. acid. base. acid. 



It is evident that 53*999 may be written 54*0 without any inaccuracy. If, there- 

 fore we add together the equivalents of nitrogen and oxygen in the ratio found in the 

 empirical formula, we shall have 



1 equivalent of nitrogen = 14 

 5 equivalents of oxygen = 40 



54 t= the atomic weight of the acid'. 



We will now consider the mode of determining the rational formula of a substance 

 from the results of the analysis and the density of the vapour. Suppose a hydro- 

 carbon to have yielded on analysis: Carbon, 85-714 ; Hydrogen, 14-286 ( = 100): 



And- L"*-I*M8 1*222-1M 



6 1 



The quotient being the same, the empirical formula becomes OH n . It remains, 

 therefore, to determine the value of ". The density of the vapour was found to be 

 2-9064. Now the hydrocarbons always possess a condensation to four volumes. In 

 the article EQUIVALENTS, CHEMICAL, rules are given for ascertaining the equivalents 

 of substances from the densities of their vapours. For four-volume formulae the rule 

 is : Divide the density of the gas by half the density of hydrogen. Applying this 

 rule, we have 



0346 



It is therefore necessary to find what multiple of the atomic weight of CH will 

 make 84-00. Now C + H = 6 + 1 = 7, and 7 x 12 = 84. Consequently, the formula is 

 12(CH), or as it is always written, C I2 H 12 . 



The above rules will suffice to enable any person to determine the empirical and 

 rational formulae of substances from the results of analysis. 



For further information on the subject of Chemical Formulae, the reader may consult 

 Watts's ' Dictionary of Chemistry.' 



FORJVIYIiE. The hypothetical base of formic acid. 



FOSSXIi. (Fossilis, anything dug from the earth.) Formerly all minerals were 

 called fossils, but the word is now restricted to express the remains of animals and 

 plants found buried in the earth. 



?OSSZZi IVORY. The bones and tusks of elephants and mammoths are found 

 in eastern Siberia, and along the shores of the Arctic sea in great abundance. The 

 tusks -are collected for sale, but are much less valuable than the recent ivory. 



FOSSIL PAPEH, or Wood, or Flax, or Cork. Terms used to distinguish familiar 

 varieties of Amianthus, according as they resemble one or other of the substances 

 named. 



FOUWDIWG- ; roUXDRY. In foundries attached to blast-furnaces where from 

 20 to 30 tons of iron are made per diem the moulds are generally mere troughs cut 

 in the sand, into which the melted metal flows and cools in contact with the air. The 

 surfaces of the castings made in this manner present appearances which vary according 

 to the quality of the iron. 



The kinds of iron adapted for founding purposes are those which are most fluid when 

 melted, and which contain most carbon, and aro called Nos, 1 and 2, They are dis- 



