Minerals from Terlingua, Texas. 265 



evidence on these points reference must be made to the full 

 report; suffice it to say here that no certain evidence was 

 obtained in favor of the presence of one or the other of these 

 elements other than in the combinations above named, though 

 the proof is not absolute that there may not be small amounts 

 of one or both (see also p. 268). If present, the hydrogen is in 

 such small amount as to be unimportant in the formula of the 

 mineral as a homogeneous unit, and oxygen must also exist in 

 all probability as basic oxygen in a minor constituent of a mix- 

 ture. The summation given on p. 267 is a strong argument 

 against the presence of considerable percentages of either. 



When, however, the mineral is fully decomposed by heat in 

 presence of lime or sodium carbonate, oxygen is liberated in 

 quantity. Theoretically the amount should be exactly equiv- 

 alent to the S0 4 and Cl 2 found in a particular sample if the 

 compound is normal and not basic, and this should afford an 

 exact means for deciding the question of the presence of oxygen. 



But as a matter of fact the oxygen never did equal the cal- 

 culated amount by several tenths of one per cent. Of the 

 various possible explanations to account for the deficiency the 

 following, based partly on qualitative tests, seems the most prob- 

 able. The oxygen is liberated partly in an active state and 

 forms a chloroxy-salt of sodium or else nitrite or nitrate of 

 sodium in small amount. It would require but little of one of 

 these salts to bind enough oxygen to account for the observed 

 deficiency. The evidence favors an oxy-salt of nitrogen in 

 preference to one of chlorine. It is, of course, assumed that 

 any such salt was formed by the act of decomposition and did 

 not preexist in the mineral. 



Analytical methods employed and the results.— ■( 1 ) Nitro- 

 gen. For nitrogen three methods were used : ( a ) expulsion 

 as ammonia by sodium sulphide and gravimetric determination 

 as the chlorplatinic salt; (5) expulsion as ammonia by ammo- 

 nium bromide in a closed vessel, collection of the ammonia in 

 titrated oxalic acid and determination of the acid left over ; 

 (c) direct determination as nitrogen gas expelled in vacuo, col- 

 lected by the aid of a To pier pump, and measured in a gas 

 burette after freeing from other gases if present. 



Numerous data are to be found in the full report relating to 

 these methods, particularly the last. The second method was 

 found to yield about two-tenths per cent more nitrogen than the 

 first or than the second when sodium carbonate was used as a 

 retainer for the chlorine and sulphur, the results by which 

 agreed well. 



This was probably in part if not altogether due to the 

 action of the clayey gangue on the ammonium bromide with 

 liberation of some ammonia (see p. 268). Were it not for 



Am. Jottr. Sci.— Fourth Series, Vol. XXIV, No. 141.— September, 1907. 

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