JOURNAL OF CHEMICAL EDUCAl
ever, the difficulty which arises when applying his rated solutions of calcium chloride or sodium chlo Rule 2 to the salts of polyfunctional acids is due to the I might have thought of these myself except, poss iact that the equation given only applies to a discrete I felt others must have experimented with them molecular fragment; one must know the number of proved them t o be of little value. Upon trial, however, I found the calcium chlorid such fragments to calculate the number of rings and multiple bonds. An alternative form of Rule 2 which lution eminently effective, and the sodium chla obviates the diEculty is: Treat each organic ion solution only scarcely less so. Chlorine could re] separately; before applying Rule 1, add one hydrogen trapped overnight. by this method, with little dissc for each negative charge, and subtract one hydrogen in the liquid by morning. Then I thought I would compare water with 1 for each positive charge. Although not stated explicitly by Gillis, it is obvious solutions. The result astonished me. I was ab: that his method must not be applied to molecular com- collect the chlorine with no trouble at all and, in : pounds, complexes, hydrates, etc., without either treat- tion, I collected one bottle of chlorine and allow, ing each portion separately or using (n - m p) for to remain in full view upon the stand in a glass the number of rings and multiple bonds, where p is the matic trough and directed the pupils' attention, I number of molecular entities in the complex. sionally, to the gradual rise of water in the bi I checked with the publishers of many of the I W. H. T. DAVISON school laboratory manuals and learned that all DUNLOP RESEARCH CENTRE the conventional air displacement method. BIRMINGHAM, ENGLAND Of course, the gas first prepared was not colle It was run into a solution of hypo as usual and all, T o the Editor: to escape in order to eliminate displaced air fron When I demonstrate to my first-term chemistry generating bottle. Carbon dioxide, by the wa classes the experiment entitled "The Preparation and collected by water displacement and chlorine is Properties of Chlorine," I tell them that the chemist slightly more than twice as soluble. I intend to us always prefers to collect gases by water displacement. water displacement method hereafter unless it ca I then state that the reasons for this preference are proved that it has undesirable features. twofold: first, since the water acts as a seal there is less likelihood for the escape of gas into the room (with MITIMNG . WO possible unpleasant effects upon the mucous membranes and lungs); second, the gas when collected by water diplacement is likely to be of higher purity. (In water displacement, when the water is out the gas T o the Editor: is in, whereas by air displacement the gas is more likely R a s h a v a is one of the famous chemical treati~ to be contaminated with air.) From the above statements I develop that it follows, ancient India. This writing has been placed not therefore, that when chlorine is not collected by water than the thirteenth century A.D. Some hist,orians displacement the gas must be assumed to be fairly sol- fer to put R a s h a v a in the twelfth century A.D uble in water and therefore has to be collected by air this work the following flame tests for metals are tioned: displacement. However, this method of collection by Copper gives a blue flame air displacement has always been distasteful t o me and .4nd tin a pigeon odor, I decided to try some liquid other than water. Lead is pale tinted Since some of this research was performed a couple of .4nd iron is dull yellowish brown. years ago I cannot remember with certainty all the liFlame tests described for other metals and ore quids with which I experimented, but the list included kerosene, mineral oil, carbon tetrachloride, chloroform, ambiguous because of defective rendering of the tr and mercury. The last-named, to my chagrin, gave me script. It seems that the author of the R a s h a v a noticed the difference in the color of metallic flz calomel. None gave me the proper results. Recently I gave renewed thought to this problem It will be interesting t o know if there is any menti and wrote t o Dow Chemical Company for guidance. flame tests in the literature earlier than RasArnaI asked them if they could suggest a liquid in which TAPANK. MUKHERJ chlorine was but slightly soluble and which did not WAYNEUNIVERSITY react with chlorine. They suggested the use of satuDETOIT, ~ 1 ~ ~ 1 0 . 4 ~
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