THE ATOMIC WEIGHTS OF BORON AND FLUORINE. 



49 



number now in use, 11.0. It will be admitted, however, that the 

 selection of the first two compounds (the sulphide and carbide) 

 and the methods of analysis seem unfortunate for the purpose 

 in view. Furthermore, Gautier himself admits 3 that the carbide 

 was not pure. 



The boron was prepared by Moissan's method and the sul- 

 phide, chloride, and bromide obtained from it were probably 

 reasonably pure. Unfortunately, however, the methods of analy- 

 sis are inadequate. The bromide of boron, for example, was 

 analyzed as follows: The compound (on the average 3.5625 g. 

 were used) was decomposed by water and the solution diluted 

 to 1 liter. Portions of 50 c.c. each were withdrawn and the hydro- 

 bromic acid determined as silver bromide. The average quantity 

 of boron tribromide actually analyzed, therefore, was only 0.1781 

 g.; the average amount of silver bromide actually determined 

 weighed only 0.4002 g., not 20 times this amount. These figures 

 (with Br = 79.92) would lead to 10.97 for the atomic weight of boron. 

 This value, however, is rendered extremely uncertain by the 

 volumetric operations and the author admits 4 that a variation of 

 fromO.6toO.7mg. ("at the most") in the weight of the silver bromide 

 was considered satisfactory. A variation of +. 0.3 mg., would 

 have caused the atomic weight of boron to vary from 10.78 

 to 11.16, whereas Gautier's own results vary only from 10.981 



3 Thecarbide of boron wae heated in chlorine 

 which removed the boron as BCh. The 

 residual carbon was burned in oxygen 

 and weighed as carbon dioxide. The 

 accompanying two experiments are 

 given by Gautier (loc. cit., p. 371). The 

 author then continues as follows: "Le 

 poids du carbone et celui de 1'acide 

 carbonique ne presentent pas une concordance absolue. Cela tient a la presence, 

 dans le borure, d'une tres petite quantite" de matiere e"trangere; le poids de 

 borure a e'te' diminue" de cette quantite" pour le calcul." (!) 



The carbon corresponding to 0.3359 gram of CO 2 is only 0.0916 gram. The total 

 amount of carbon actually found was 0.0941 g., or 0.0025 g. in excess of the 

 theory. In other words, after removal of the boron as BC1 3 , the total carbon 

 left behind in two experiments contained 0.0025 g. (=2.66 percent.) of an 

 unknown impurity which was subtracted from the original weight of the boron 

 carbide! 



*"Pour determiner la quantite" d'acide bromhydrique contenu dans les solutions 

 obtenues, nous avons fait chaque fois deux determinations simultane'es sur Z V du 

 volume total, soit sur 50 c.c., et nous n'avons conside're' I'experience comme 

 valable que lorsque le poids de bromure d'argent obtenu pour chacune d'ellea 

 ne differait que de T % a T 7 5 de milligramme au plus." (Loc. cit., p. 377.) 



