2 G. Bams — JExperiment with Liquid Carbon Dioxide. 



CO2 tube is clear, and the demarcation between liquid and 

 vapor broad and unmistakable even at a distance. Moreover 

 the tube acts like a cylindric lens, a sharp silvery focal line 

 being obtained both for the liquid and the gaseous part. 

 The two focal lines, however, are not coincident, and hence, 

 thQ projecting lens must he moved hack and forth to obtain 

 sharp images of the linear foci corresponding to the vapor or 

 the liquid, respectively. This motion is considerable, two or 

 more inches with the usual tube ; and inasmuch as the inner 

 ends of both focal lines terminate on projection in the visible 

 meniscus, I have based the following experiment on this 

 observation : 



D 



D 



50 



^._3J0 



5 cm. 



The figure shows the disposition of apparatus in sec- 

 tional plan through the middle of the (vertical) CO2 tube. 

 AaAa is a trough with vertical wooden sides A A, about 

 a foot square and placed about 2 inches apart internally. 

 The ends, through which sunlight L is to pass horizontally, 

 are closed by strips of thick plate-glass a^ a, and the non-con- 

 ducting lid (not shown) is removable. The center of one of 

 the wooden sides A contains a hole and receives the perforated 

 cork B, in which a horizontal rod or axle suitably holding the 

 carbon dioxide tube d, is free to rotate. The tube being thus 

 revolable on a horizontal axis, the small viscosity of the liquid 

 as compared with water is well shown in projection by inverting 

 the tube rapidly. The millimeter scale e, on transparent glass, 

 is fixed in the same vertical plane with the tube and projected 

 with it to measure the expansion. A thermometer is placed 

 at some point t. A wide stop-cock C, inserted near the 

 bottom of the trough, allows the admission of either warm or 

 cold air, or if need be, of water. The thermometer is only 

 needed to calibrate the CO^ tube and scale in terms of 

 temperature, by using the trough as a common water-bath. 

 After this, the thermometer may be dispensed with, since the 

 tube and scale constitute a more sensitive and a more easily 

 visible instrument. 



2> Z> is an opaque screen with an aperture small enough to 

 cut off all rays except those which pass through the lens 

 F. The latter was of about 55°"" focal distance, 10' 



in 



