175 



CRniciSM OF AN Experiment Used to Determine the CoxM- 

 BiNiNG Ratio of MA(iNESU.M and Oxyuen. 



James H. Ransom. 



Ill some of the niodeni lal (oratory iiiuiiuals for use in iieiieral chem- 

 istry work ail exiierimeiit is descrilied whereby a wei.uhed amount of 

 mayiiesium iiowder is oxidized in a covered rrucilile until a constant 

 weight is obtained. The increase in weiiiht has liecii assumed to l»e due 

 to (ixy.ii'cn. and tlius tlie ratio of the two elements in the oxide easily 

 calculated. 



My students have pi-rfoimed this experiment duriiiL;- tlu' last two years 

 but have not been alile to secui-e sutticiently coiicordani results t(( make 

 it apiiear to them as illustratin.i;- the law of constant comiHisitioii. 



Foiiie observations are readily made in perforniin.u- tlie experiment. 

 The pioduct. except perhaps at the surface, is not white, as is niaiiiie- 

 siuiii oxide, but of a .uray color, due evidently to a mixture of substances 

 of different colors. Also the crucililes at the end of the experiment are 

 coated within with a black substance which can not be rem ived even ou 

 scouriiift' with sand: and tlie crucibles lose in weight. 



Examination of the product of burning shows that on treatment with 

 small amounts of water ammonia is evolved, tlius indicating that m.ig- 

 nesiuiii nitride is one of the substances present. As in this compound 

 the ratio of the elements is 1:888 while in the oxide it is l;(i(;T it follows 

 that from this standpoint the increase in weight niusi lie less than the 

 theory. Again, on treating the product with fairly concentrated hydro- 

 chloric acid a disagreealily odorous gas is evolved which at times is spon- 

 taneously eoml)ustible. It is. without dould. hydrogen silicide from mag- 

 nesium silicide formed Ity the action of magnesium on the crucible ma- 

 terial. On treating with acid as above described there always remains 

 a black insoluble amorphous residue mixed with white particles which 

 under a handdens look like silica. The lilack mass when heated ou 

 platinum foil changes to a white i)owder which resembles silica. Appar- 

 ently the black portion is silicon. It is conceivable that a part of the 

 silicon after lieing formed, and during the heating, is oxidized by the air; 

 and as it unites with nearly twice as much oxygen as does the same 

 weight of magnesium, it might equalize the loss of the oxygen content 

 due to the causes already indicated. Thus can lie explained the nearly 

 theoretical results so often obtained. But at best these results must re- 



