108 SOME PRINCIPLES AND METHODS OF ROCK ANALYSIS, [bull. 176. 
ammonia, cither in the form of chloride or sulphate, or even as free 
ammonia, was given oil' on heating. Its appearance was not limited 
to one or a few specimens of a series, but seemed to be characteristic 
of all, and to be afforded by the unbroken rock as well as hy the 
powdered sample. The precise conditions under which the specimens 
were collected not being known, it is impossible to affirm positively 
that the ammonia may not have been due to recent organic contamina- 
tion of some sort, especially in the case of the slates, but it is believed 
that a more critical collection of material will not alter the general 
result. Its amount was sometimes readity determinable by Nessleriza- 
tion, being as high as 0.04 per cent in some slates. Carbonaceous 
organic matter was absent from most of these, but doubtless existed 
in them in their early history. In their case the ammonia was, in part 
at least, evolved as such, imparting a strong alkaline reaction to the 
water in the upper part of the tube.. The presence of sulphides, 
fluorides, or chlorides in the rock might cause the ammonia to appear 
as a sublimate of sulphate, fluoride, or chloride. Speculation on this 
matter would he altogether premature, but attention is called to it in 
the hope that other observers may be led to look for and investigate 
similar appearances. It should be borne in mind that the nitrogen 
present would not necessarily appear as ammonia or ammonium salts, 
since it might be given off in the elemental condition, as with the gases 
obtained from uraninite. 
XXVII. SPECIAL OPERATIONS. 
The problem often presents itself of ascertaining the composition of 
that portion of a rock powder which is soluble in special reagents or in 
a reagent of a particular concentration. No precise directions can be 
formulated to meet such cases. The procedure must vary with the 
character of the constituents of the rock and with the object which it 
is sought to attain, and only in exceptional cases can a separation of 
this kind be sharp. Much depends on the degree of fineness of the 
powder and on the length of time it is exposed to the action of the 
reagent. 
DETECTION OF NEPHELINE IN PRESENCE OF OLIVINE. 
For confirmation of the microscopic diagnosis, Prof L. V. Pirsson 1 
has indicated a means of detecting nepheline in presence of olivine, as in 
nepheline basalts, based on the very ready solubility of nepheline, as 
compared with olivine, when boiled for but one minute with a sufficiency 
of very dilute nitric acid (1:40). Gelatinization of the filtrate on evap- 
oration is taken as evidence of the presence of nepheline. If olivine 
1 Am. Jour. Sci., 4th scries, Vol. II, p. 142, 1896. 
