Experiments and Obfervathns, &c. 33 1 



In the pirecedirig procefs, the greateft care mould be taken 

 that no ir rtri be fullered to come in contact with the colour; 

 for the gallfc.acid or aftringent principle, which eminently 

 abound in this vegetable, will inftantly difiblve iron^ and the 

 fmalleft particle of that metal is fatal to the delicacy of the 

 weld yell 



ow 



LIV. Experiments and Obfervatitms on certain^ Stony and 

 Metalline Subjiances luh'nb at different Times are J aid to 

 have fa'. 1 n on the E :rlh ; alfo en various Kinds of Native 

 h-.n, Bj Edward Howaiid, Efq. F.R.S. 

 [Continued fnjiij p. 224.] 



rT ^ Examination of the Stone from Sienna. 



I HE external coating of this (lone appeared to have the 

 fame characters as that of the ftone from Benares. 



The pyrites, although certainly p relent, were not cryftal- 

 lizecl in fuch groups as m the preceding ftone; nor could 

 they be feparated by mechanical means. 



The attractable metal was eafily feparated by the magnet; 

 but 8' grains only were collected." I treated them with nitric 

 acid and ammonia, as in the preceding cafe. Nearly one grain 

 of earthy matter was mfoluble; the weight was therefore re- 

 duced to rather lefs than eight grains. The oxide of iron, 

 precipitated by ammonia, weighed eight grains ; and the fa- 

 line liquor gave abundant indications of nickel. As eight 

 grains of this oxide of iron contain nearly fix of metal, the 

 quantity of nickel in the bare eight grains may be estimated 

 between one and two grains. Some globular bodies were 

 extracted, but too few to analyfe. 



Since the pyrites could not be feparated, I collected 150 

 grains of the ftone, freed from iron by the magnet, and a? 

 exempt as pofTible from globular bodies. Theie J50 grain. 5 * 

 I firft digeftcd with muriatic acid, that the pyrites might be 

 decomposed, and every thing taken up which could be dif- 

 folved by that menftruum. A very decided difengagement 

 of fulphureted hydrogen gas was occafioned. When the acid 

 could produce no further aftion, I collected the undiifolved 

 matter on a filter, and boiled it with the moft concentrate 

 nitric acid, in hopes of being able to convert the fulphur, 

 previoufly liberated, into futphuric acid : but my endeavours 

 were fruitlefs ; for, upon the addition of nitrate of barytes 

 to the nitric folution, rendered previoufly tranfparent, a very 



infignificant 



