144 



THE POPULAR EDUCATOR. 



which at first sight appear inexplicable can not only be readily 

 retained and understood, but the possession of the radical will 

 give the power of building up the ether, the alcohol, the acid, etc., 

 belonging to it ; exactly as the root of a word being given, the 

 noun, the verb, the adverb, etc., can easily be arrived at. 



Our space, however, being limited, we consider that it will be 

 more beneficial to our readers to enter into the properties and 

 composition of the various products of the animal and vegetable 

 kingdoms which we meet in our daily life, than to dwell on the 

 classification of formulae, referring the student to the third 

 volume of Miller's " Elements of Chemistry" for a full discussion 

 of the subject. 



Organic Analysis. Since carbon and hydrogen are the staple 

 constituents of organic bodies, the quantities in which they are 

 present are always estimated by the combustion of the body in 

 the presence of oxygen. By this means the carbon is converted 

 into carbonic acid gas, and the hydrogen into water. The 

 means by which this is effected may be thus indicated : A tube of 

 hard Bohemian glass is arranged on supports, as in Fig. 54, in a 

 trough of sheet iron. The tube is open at B ; its other extremity 



Fig. 51. 



is drawn out into a point, F, and bent obliquely. The body 

 to be analysed is carefully dried. The substance from which 

 oxygen is furnished for the combustion is cupric oxide. This is 

 freshly made, and heated to expel all moisture. A quantity is 

 placed in the combustion tube, sufficient to fill some two inches 

 of its extremity, A. The body to be analysed is carefully 

 weighed (about 6 grs. is usually taken) ; then it is mixed with 

 some of the cupric oxide in a mortar. With the greatest caution 

 it is introduced into the combustion tube. The mortar is rinsed 

 out with more oxide, which is also placed in the tube. The tube 

 is now filled to within two inches of its opan end with pure 

 oxide; c, a calcium chloride tube for collecting the moisture, 

 and D, Liebig's potash bulbs for absorbing the carbonic acid gas, 

 both accurately weighed, are attached to the tube by a tightly 

 fitting cork. 



Hot charcoal is now placed in the trough at A. When the 

 tube is here red-hot the partition, E, is gradually moved towards 

 B, so that the whole tube is by degrees brought to a red heat. 

 At this temperature the carbon and hydrogen of the organic 

 body take oxygen from the cupric oxide. The water thus 

 formed is absorbed by the calcium chloride, and the potash 

 retains the carbonic acid. When the latter ceases to appear in 

 the bulbs, the point F is broken, and by means of the mouth a 

 gentle suction is applied to the open end of the potash bulbs, so 

 that air is gradually drawn through the combustion tube, which 

 brings with it the last traces of carbonic acid. The apparatus 

 is now dismounted, and in about an hour the tube C and the 

 bulbs D are weighed ; | of the gain c has experienced indicates 

 the quantity of hydrogen, and of the gain of D gives the 

 quantity of carbon, the body contained. 



If the body contain nitrogen, a separate analysis is required to 

 determine its quantity. But in this case a precaution is neces- 

 sary in the process above described. When nitrogen is heated 

 with cupric oxide, a certain quantity of some of the lower oxides 

 of nitrogen comes off. This the chloride of calcium would 

 retain ; hence the end of the combustion tube is packed for six 

 inches with copper turnings, and these are kept red-hot. By 

 this means the oxides of nitrogen are decomposed, the copper 

 combining with the oxygen, and the liberated nitrogen passing 

 forward. 



The determination of the quantity of nitrogen is based upon a 

 fact observed by Gay Lussac, that if nitrogenous bodies be heated 

 with an excess of potassic or sodic hydrate, all the nitrogen 

 comes off in combination as ammonia. 



To take advantage of this transformation, the body is intro- 



duced into the combustion tube as before, but not mixed with 

 cupric oxide, but with soda-lime a compound procured by 

 slaking well-burnt lime with a solution of soda, then evaporating 

 and igniting. The drying tube, C, is dispensed with, and bulbs 

 somewhat similar to D are charged with pure hydrochloric acid. 

 The heat is applied as before. The hydrochloric acid retains 

 the ammonia. After the process is complete, and air has been 

 drawn through the apparatus in the usual way, the bulbs are 

 emptied, and carefully washed out, first with a mixture of 

 alcohol and ether, and then several times with water. A solu- 

 tion of platinic chloride is now added, and a double chloride of 

 platinum and ammonium is precipitated. This is repeatedly 

 washed with a mixture of alcohol and ether, to remove any 

 trace of platinic chloride. It is now brought in a weighed filter 

 and again washed ; then dried in a water bath and weighed. 



220'52 parts of the salt are equivalent to 14 of nitrogen. 



The result of such analyses is to give the percentage com- 

 position of the compound. 



An example will best indicate this : 4'750 grs. of sugar were 

 analysed 



Grains. 



Potash bulbs weighed after experiment . . 781 '13 

 before . 773'82 



Carbonic acid = 7'31 



Calcium chloride tube after experiment . . 226 '05 

 before . . 223-30 



Water 275 



7 '31 x = 1-994 = Carbon. 

 275 x - = -3056 = Hydrogen. 

 Or, calculating this for 100 parts of sugar, we have 



Grains. 



Carbon 41-98 



Hydrogen 6 '43 



Oxygen (by difference) . . 51 '59 



100-00 



From this, to construct the empirical formula, it is necessary 

 to divide each of the quantities by the atomic weight of the 

 element : 



41-98 6-43 51-59 



-^ = 3-49; ^ = 6-43; -^ = 3-22. 



That is 



319 equivalents of . . Carbon. 



643 . Hydrogen. 



322 . . Oxygen. 



Allowing for experimental errors, evidently the number of 

 atoms of hydrogen double those of the oxygen ; and the oxygen 

 to the carbon bears a proportion of nearly 11 to 12 ; so that the 

 empirical formula is C^H^On- The number of these elements 

 may be only multiples of the real numbers. They cannot be 

 less than they are, because any division of the whole three 

 would produce fractions ; and as atoms are indivisible, a frac- 

 tional atom cannot exist. 



To decide the true or rational formula, two ways suggest 

 themselves. 



1. A compound of the organic body with some inorganic 

 element is analysed ; and, knowing the atomic weight of the 

 latter, we thus discover the combining weight of the molecule of 

 the organic compound. 



2. We know that the density of a volatile organic compound 

 is half its molecular weight, just as the density of CO, is 



= 22 ; that is, the molecule of C0 2 weighs 22 times the atom 



m 



of hydrogen. 



So is it with any other volatile organic body. 



Thus, by accurately weighing a glass globe filled with the 

 vapour, and finding the capacity of the globe, the density is 

 ascertained; twice this gives the molecular weight, and thus 

 the rational formula is fixed. 



For the details of these processes larger works must be con- 

 sulted. Liebig's " Hand-book of Organic Analysis " is record- 

 mended. 



