The answer to this question comes immediately after quite a thorough description of Dr. Heidegger's room. We are presented with the dominating portrait of Sylvia Ward and the sad tale that accompanies it and other more unsavoury aspects of his room, such as a skeleton, that clearly place Dr. Heidegger as a man of knowledge and experimentation. Then we are given a description of this small table, which has clearly been set up for the experiment that Dr. Heidegger wishes to perform:
On the summer afternoon of our tale, a small round table, as black as ebony, stood in the centre of the room, sustaining a cut glass vase, of beautiful form and elaborate workmanship. The sunshine came through the window, between the heavy festoons of two faded damask curtains, and fell directly across this vase, so that a mild splendour was reflected from it on the ashen visages of the five old people who sat around. Four champagne glasses were also on the table.
Note how the beauty of the vase points towards the value of the liquid contained within it. Also it is clear that the description of the sunlight falling on the vase likewise emphasises its importance, foreshadowing its effect as a "mild splendour" from the vase is reflected onto the withered faces of the guests and Dr. Heidegger.