OASOMETRIC ANALYSIS. 



BATranro. 



524 



The operation* just described give us the following four data from 

 * hi. -h it is easy to determine the respective volumes of two or mora 

 of the four gases present in the mixture : 



1. The volume of the gas taken for analysts. . . = A 



2. The volume of the combustible gases present . . = A' 



3. The contraction of volume on explosion . . . = C 



4. The volume of carbonic acid generated on explorion = D 



It will be seen that the value of A' is ascertained by deducting from 

 A the volume of nitrogen in the mixture, determined as just described. 



The respective volumes of the three combustible gases are deter- 

 mined from the consideration of the contraction, anH the volume of 

 carbonic acid, produced by each on explosion, with excess of oxygen, 

 a* seen in the following table : 



If we now represent the volumes of nitrogen, hydrogen, carbonic 

 oxide, and light carburetted hydrogen respectively by the letters v, x, 

 y, and 2, we have, taking the data just given, the following equations, 

 expressing the volume* of the four gases present in the mixture 

 submitted to analysis ; 



=A A' 

 X=A.' D 



3V-2C + D 



8 



__ 2p 8 



If, on the application of these formula; to the result* of an analysis, 

 the value of any letter be either a small negative quantity or = 0, it 

 follows that the gas denoted by the letter is not present in the 

 mixture. 



The only difficulty likely to arise in making such indirect determi- 

 nations, consist* in adding neither too much nor too little oxygen to 

 the combustible gas, since, when too much U added, either no explosion 

 ensues on passing the electric spark, or, if the ignition of the mixture 

 be effected, and light carburetted hydrogen or carbonic oxide be 

 present, the temperature is too low to ensure the complete oxidation 

 of these gases ; whilst when too small an excess of oxygen is added, 

 the violence of the explosion is so great as to endanger the rupture of 

 the glass tube containing the gases. It is not difficult to avoid these 

 contingencies where the nature of the gaseous mixture experimented 

 upon is approximately known, if it be borne in mind that, of the three 

 combustible gases above mentioned, each volume of hydrogen or car- 

 bonic oxide requires about 1J volumes, and each volume of light carbu- 

 retted hydrogen about 6 volumes, of oxygen, for successful combustion. 



We have thus given a very condensed account of this branch of 

 chemical analysis ; but for more minute details the reader is referred 

 to the article ' Analyse fur Close ' (by the writer of the present article), 

 In the ' Handwbrterbuch der Chemin,' by Liebig, Poggendorf and 

 Wohler, 2tc, Auflage. In conclusion, and as on illustration of the 

 application of these analytical processes, we shall now describe the 

 mode of performing an analysis of coal gas. 



Analyiu of Coal Gat. Purified coal gas generally contain* the whole 

 of the following ingredients : 



1. defiant gas and analogous hydrocarbons. 



2. Light carburetted hydrogen. 



3. Hydrogen. 



4. Carbonic oxide. 



5. Carbonic acid. 



6. Oxygen. 



7. Nitrogen. 



Of these ingredient*, the first, fifth, and sixth are determined by the 

 direct, and the rest by the indirect, methods above described. 



Two or three cubic inches of the gas are passed into the tube j, and 

 subsequently into r, for measurement. The oxygen, carbonic acid, and 

 defiant gas are now successively eitimated in accordance with the 

 method* described under the head of Direct Dtierminatimi : the mode 

 of absorbing olefiant gas there given also effects the simultaneous 

 removal of the analogous hydrocarbon*, to which, in part, the dimi- 

 nution in volume will therefore be due. The remaining gas muat now 

 be exploded with about three times its volume of oxygen, and the 

 respective volumes of the four remaining gases determined as described 

 under Indtrtrt Delrrminationi. 



This estimation of the relative quantities of the several constituents 

 of coal gas doss not give any absolute data from which the illuminating 

 power and consequently the commercial value of coal gas can be calcu- 

 lated. It give* us, it is true, the amount of illuminating hydrocarbons 



(olefiant gas and analogous hydrocarbon*) to which exclusively the il !u ' 

 minatiug power of coal gas is due ; but as these vary in their light-giving 

 powers in direct |>roportion to their richness in carbon, it follows tht 

 their value can only be estimated by determining the amount of ca r - 

 bon which a given volume of them contains. This can easily be effected 

 by the additional operation of ascertaining the amount of carboni 

 acid generated by a given volume of the coal gas on explosion with 

 oxygen, and comparing this with the amount produced on the explosion 

 ui 1 1,.- rusidual gas remaining after the abstraction of the hydrocarbons. 

 For this purpose a known volume of the original gas is introduced into 

 r (toeji'i. ooL 820), and mixed with five times its bulk of oxygen : the 

 electric spark is pawed, and the volume of carbonic acid general 

 the explosion ascertained by absorption with caustic potash in J. If we 

 now denote the per-oentage of hydrocarbons absorbed by anhydrous 

 sulphuric acid by A, the volume of carbonic acid generated by 100 

 volumes of the original gas by B, the carbonic acid formed by the com- 

 bustion of the non-luminous constituents remaining after the abs 

 of hydrocarbons from the above quantity of original gas by c, anil the 

 volume of carbonic acid generated by the combustion of the luminife- 

 rous hydrocarbons by x, we have the following equation : 



x=s c 



Consequently, the amount of carbonic acid generated by one volume of 

 the hydrocarbons will be represented by 



B o 

 A 



Now, as the amount of carbon iff each volume of the illuminating 

 hydrocarbons is directly proportional to the volume of carbonic acid 

 which these hydrocarbons produce on combustion, it follows that the 

 formula just given expresses the illuminating power of the gas. For 

 comparison, it is convenient to take as a standard the illuminating or 

 carbon value of olefiant gas, which generates twice its own volume of 

 carbonic acid. In order, therefore, to express the value of the lumini- 

 ferous hydrocarbons of any sample of gas, in units of olefiant gas, it is 

 only necessary to change the last expression into 



B c 



2A 



Thus, any sample of gas containing 10 per cent, of hydrocarbons, of 

 which one volume generates three volumes of carbonic add, will have 

 an illuminating effect equal to another gas containing 15 per cent, of 

 olefiant gas. This method, therefore, furnishes us with an exact 

 chemical standard of comparison for the illuminating vahu> <' 

 description of coal or other gas in use as a source of artificial light. 



GAUGING is the method of determining by actual measurement 

 the number of gallons contained in any vessel intended to hold goods. 

 The greatest use of this art is in the collection of the revenue, in 

 which it is necessary to measure the bulk of vessels without disturbing 

 their contents. For this purpose a number of rules have bet ; 

 down by various writers, of whom the reader who is interested in the- 

 subject may consult Leadbetter's ' Treatise on Gauging,' John ' 

 ' Young Mathematician's Guide,' or Dr. Hutton's ' Mensuration.' The 

 iid down were, in many coses, of uncertain application ; as, for 

 instance, a close cask was to be treated either as a frustum of a 

 Hpheroid, or of a parabolic spindle, or as a double frustum of a para- 

 boloid, or else of a double cone, according to its appearance. The 

 allowance made for the thickness of a cask was a guess, and the 

 method of using small sliding-rules, to which supervisors fonix-rly 

 renorted to escape calculation, is a species of estimation which would 

 never have been tolerated in money transactions between man and 

 man. The inference to be drawn from the art as described by early 

 writers, is that, generally speaking, the results of excisemen's measure- 

 ments were below the truth : had it been otherwise, the fact could not 

 but have been known to merchants and tradesmen, who can gauge 

 their own vessels after the content* are removed, or who learn their 

 bulk in the removal. If the methods of the excisemen were Uilur.il>] v 

 uniform, which ia perh nearly true, ii w. from 



writers on the subject, no injustice was done by unequal taxation, and 

 the government would probably have found it as easy to inert 

 duties, on to raise an additional revenue from a more correct method 

 of collecting the old one. 



With larger sliding-rules for calculation, and the aid of habit derived 

 from experience, it is possible very accurately and easily to measure 

 casks which do not depart much from a given standard of form, 

 is what is done by gaugers at the present time; and their practice box 

 attained considerable accuracy. In a particular instance which ha* 

 come to our knowledge, and in the case of a vat which held 6500 

 gallons, the measurement of the exciseman did n.it. <lin.-r more than 

 ten gallons from the truth. Tlii* degree of accuracy 

 modern, and must in a considerable degree arise from similarity <>t 

 form being very nearly preserved in the different species of casks. 



The great variety of cases which occur would make a summary 

 inconveniently long. Wherever a content H to be found, eitli 

 figure itself is simple and regular, as in the case of a cylinder, or nearly 

 a simple figure, as in the case of some casks, which may be considered 

 a* the frusta of spheroids [sec BARREL as an instance of the approxi- 

 mating supposition], or so irregular that the content can only be found 



