LIMESTONES. 597 



REMARKS ON TABLE V. 



The carbon dioxide and the water of the above analyses were estimated as in 

 the case of the eruptive rocks; the one by loss in weight upon treatment with hydro- 

 chloric acid iu a suitable apparatus, the other by absorption in a calcium chloride 

 tube. 



The organic matter of Analysis II was determined by an ordinary combustion 

 analysis, after dissolving a considerable quantity of the rock in dilute hydrochloric 

 acid and collecting and drying the insoluble matter upon an asbestus filter. The car- 

 bon dioxide formed was caught in potash bulbs nnd weighed. For 58 parts of carbon 

 found, 100 parts of organic matter were assumed, as recommended by Freseuius. 



The trace of iodine shown in Analysis I was detected and estimated by dissolv- 

 ing one pound of the dolomite in nitric acid, precipitating the chlorine and iodine as 

 silver salts, reducing the latter by zinc and sulphuric acid, separating the iodine by 

 addition of potassium nitrite, collecting it in carbon disulphide, and titrating with a 

 dilute solution of sodium hyposulphite. Bromine could not be detected. The chlorine 

 was determined on from five to ten grams of rock by pi-ecipitation with silver nitrate 

 from a nitric acid solution. 



The alkalies were estimated by igniting twenty grams of the finely powdered 

 rock in small portions in a platinum crucible to expel carbon dioxide, extracting with 

 water and proceeding as in ordinary alkali determinations. As the amounts of alka- 

 lies found did not exceed those required by the chlorine to form chlorides, but rather 

 fell slightly below, due perhaps to partial volatilization during the preliminary calci- 

 nation, it seems probable that the chlorine is combined with sodium and potassium, 

 and possibly small quantities of calcium and magnesium. 



It was found that by boiling the powder with water without previous calcination 

 a portion of the chlorine and alkali could be extracted, and that the amount increased 

 as the pulverization was more perfect. The total amount of chlorine thus capable of 

 extraction never equaled that actually present in the rock, however. Microscopical ex- 

 amination showed the dolomites to be full of extremely minute fluid inclusions. If the 

 chlorine was derived from these inclusions, where it might be held as sodium and po- 

 tassium chlorides, a ready explanation is afforded for the incomplete extractibility of 

 the chlorine by boiling water. By no mechanical pulverization could such a perfect 

 subdivision of the particles be effected as to expose all the inclusions; a considerable 

 proportion would still remain intact and retain a corresponding amount of chlorine. 



