Chain reaction of hydrogen and chlorine initiated by HeCd laser

Changes made to improve performance, to reduce probability of destructive detonation.

For purposes of 20100730 eChem video, try to show acid gaseous product using pH paper wafted at the top of the tube. Tried, but not successful. Color change is rapid using basic fumes, but slow using acid fumes. Tried both wet and dry paper, Litmus and pH paper both were tried. Did not find blue litmus for the test.
rev: 20100805