12 THE GASES IN ROCKS. 



METHOD OF PROCEDURE. 



To obtain the gases for these investigations, the general methods of 

 Graham, Mallet, and Wright were adopted, though the details of the appa- 

 ratus were modified in many particulars. The gas is extracted from the 

 rock material which has been finely pulverized, by heating the powder in a 

 vacuum. For this purpose an apparatus consisting of a combustion-tube 

 connected with a mercury-pump capable of producing and maintaining a 

 vacuum of a fraction of a millimeter pressure is required. Simplicity being 

 desirable in order to insure the uniform working of the pump in the pres- 

 ence of corrosive gases, such as hydrogen sulphide and sulphur dioxide, 

 which attack and befoul the mercury, the most elementary type of Topler 1 

 pump was used in these experiments. 



To the receiving end of the pump a long, horizontal, calcium chloride 

 drying-tube is fused. The ideal method would be to seal the combustion- 

 tube containing the rock powder directly to the free end of this drying- 

 tube. But inasmuch as the pump and drying-tube are both constructed 

 of soft glass, whereas the tube in which the high-temperature combustions 

 are to be made must, of necessity, consist of the most refractory glass, which 

 can not be readily united to the fusible glass, one break in the system is 

 unavoidable. This is made at the end of the drjdng-tube, which is ground 

 so as to receive a tightly fitting hollow stopper of the same hard, blue 

 Jena composition tubing as the combustion-tube. A 5-millimeter tube of 

 blue Jena glass joins the combustion-tube to the stopper, and is taken of 

 sufficient length to allow of repeated cutting and resealing to successive 

 tubes, as they become useless from slow deformation under the combined 

 influence of high temperature and vacuum. 



The capillary exhaust-tube of the pump, dipping under mercury in 

 a trough, is bent upward at its lower extremity, so as to deliver the gas 

 expelled from the pump directly into the receptacle designed for holding 

 it. For this purpose, a separatory funnel of about 125 cubic centimeters 

 capacity, held by a clamp in an inverted position over the mercury trough, 

 proved most serviceable. 



In making an analysis, the rock specimen is first reduced to a powder 

 of sufficient fineness to pass through a sieve of 30 meshes to the inch. A 

 portion of this powder, roughly estimated to approach the maximum 

 quantity which can with safety be placed in the combustion-tube, is then 

 weighed and carefully poured into the tube through the hollow stopper, 

 which, on account of its shape, serves as a funnel. Because the rock-dust 

 in falling becomes somewhat packed, the tube must afterwards be held in 

 a horizontal position, and gently shaken or tapped, to establish a free pas- 

 sageway for the gases, extending the entire length of the tube ; otherwise, 

 upon attempting to exhaust, preparatory to heating, the air entrapped 

 in the powder, having no avenue of ready escape, will expand so rapidly 

 as to force some of the material into the drying-tube. 



Thus carefully filled, the tube is placed in the combustion-furnace, 

 which stands upon a table of height such that the stopper end of the com- 



1 Described by Travers, A study of gases, pp. 5-10. 



