File:Double flask gas atom diagram.png

English: Figure 18.1 shows a diagram with five pairs of circles. All of these circles are open. The left one opens on the right and the right one opens on the left. They are connected with lines at their open points. One pair is located on the left and between their two connecting lines is a black dot with a red vertical line going across. The other four pairs arranged in a column are located on the right and between the connecting lines of each pair is a a small circle with a red horizontal line going through. A right arrow labelled Open Stopcock links the pair sitting on the left to the four pairs on the right. Each of these five pairs has two dots (green and blue) arranged in different patterns. For the pair on the left, the two dots, sitting obliquely, appear only in left circle. The green dot is at the left upper part of the circle and following it the blue dot is close to the bottom right. The first pair on the right has the similar situation. The only difference is that the green dot is at the right upper part of the circle and the blue dot is close the middle left. The second pair has a green dot in the centre of the left circle and a blue dot in the centre of the right circle. The third pair has a blue dot sitting at the left upper part of the left circle and a green dot sitting close to bottom right of the right circle. For the last pair, the two dots appear in oblique direction only in the right circle. A green dot is at the right upper part of the circle and a blue dot is close to bottom left.