AS OBSEEVED IN TOEEICBLLIAN AND OTHEE VACUA. 
151 
present time retains the same appearance, showing the blue tongue expanded or con- 
tracted by the magnet in a very beautiful and clear manner. 
91. Iodine, No. 70. — Crystals of iodine were placed in a sealed glass bulb within the 
tube with caustic potassa ; it was then charged with carbonic acid gas and exhausted as 
before ; the cloud-like stratifications appeared in about eleven days ; the bulb was broken 
and the heat applied to a few of the crystals of iodine ; at first a wave discharge was 
visible, passing through the vapour without stratifications ; in a few days stratifications 
were visible, and the tube has remained ever since in the same state. If the contact 
breaker is pressed so as to cause a more sudden disruption in the discharge, a wave line 
brilliantly illuminated can be obtained, passing conjointly with and through the narrow 
stratifications, as in the arsenious-acid tube (89). When the discharge is taken from 
one terminal in vapour of iodine, the difference of the action between the outer and 
inner terminal is very remarkable ; when the former is positive, if the tube is grasped by 
the hand, the discharge shows stratifications between the hand to the discharging wire ; 
from the inner terminal no stratifications can be seen, but only a faint luminosity divisible 
by a magnet. 
92. Pentachloeide of Antimony, No. 71. — The small glass bulb containing the 
pentachloride having been inserted in the tube as in the previous experiment, was broken 
after the cloud-like stratifications had appeared, when all trace of stratification ceased, 
the discharge passing in the form of an intensely brilliant wave line ; the gradual pro- 
gress first to the narrow and ultimately to the cloud-like stratifications was subsequently 
very slow, for it was upwards of two months before the latter appeared. 
93. Bichloeide and Bisulphide op Caebon, Nos. 73 & 74. — These were introduced 
into the separate tubes in glass bulbs, as in the previous experiments ; the bulbs were 
broken as before after the discharges had assumed the cloud-like appearance ; but 
although eveiy means was adopted, first by melting the potash, and then applying 
freezing mixtm’es to condense the vapour, it remained under every condition so dense, 
that, after the glass bulbs were broken, the discharge could not pass even in the form of 
the wave line. 
All the experiments hitherto described were made in glass tubes of about I inch 
internal diameter, similar to those of my previous experiments with Torricellian vacuums, 
in which I had been necessarily limited as to the size of the tubes by the difficulty of 
manipulating with large masses of mercury ; with carbonic-acid vacua this difficulty no 
longer arose, and I was induced to try the effect that could be obtained in larger vessels. 
94. Fig. 10, Plate IX. represents a large glass vessel, egg-shaped, the globular portion 
being 18 inches in length and 7 inches in diameter ; the wires are 22 inches apart, the 
caustic potash being placed in the narrow end ; total length 25 inches. It was charged 
with carbonic acid and exhausted in the usual manner ; a portion of the potash being 
heated by a spirit-lamp, in about two months the discharge assumed in a very marked 
manner the character of large and distinct clouds, most clearly and separately defined ; 
