STALACTITES. 



Bv GEORGE H. MARTIN. M.A.. F.C.S. 



It is a matter of common experience in everyday 

 life that when an article ap^pears to be hopelessly 

 lost, it is often found again in the process of looking 

 for something else. So also in the domain of science, 

 when experiment after experiment has failed in the 

 search for the constitution of a compound for a method 

 of preparing some substance on an advantageous 

 commercial basis, or what not, the clue to the problem 

 is frequently found in the course of an entireh' 

 different investigation. 



In the case in point, for example, attempts were 

 being made, in connection with a course of lessons 

 in Elementar\- Geologv. to prepare stalactites in 

 the laboratory. The process seemed simple enough : 

 all that was necessarv, theoretically, was to allow a 

 solution of bicarbonate of calcium to drop slowly 

 from a small aperture and patienth" to await results. 

 Nothing, however, happened, although the experiment 

 was tried in several wavs. About the same time, 

 for a different purpose, a burette full of lime-water 

 was so arranged that the lime-water dropped from it 

 with extreme slowness. This experiment also failed ; 

 but for some reason the apparatus was not dismantled, 

 and the burette was left for some weeks with the 

 lime-water still dropping slowlv. When, however, 

 the burette was again examined, it was noticed that 

 a slight deposit was forming around the aperture of 

 the nozzle, and it seemed just possible that if the 

 process were allowed to continue a stalactitic growth 

 might form at the end of the burette. 



And so it proved, — a strange result when one 

 considers that of the two experiments, one of w hich 

 was started in the hope of making a stalactite, this 

 was the one that was not begun for that purpose. 



The growth of the stalactite was watched with 

 much interest, and it proceeded with comparative 

 rapidit}-. At the end of six months it had reached a 

 length of one inch and a half, which means a growth 

 at the rate of yln inch per dav. The stalactite grew 

 in the form of a hollow tube, not quite straight but 

 gently waved (see Figure 1), and of approximately 

 the same diameter throughout its length. The 

 growing end of the tube was fringed with tiny fern- 

 like projections which clasped the pendant drop as a 

 jewel is grasped by its setting. Through a microscope 

 it presented a beautiful appearance. 



The projections were then seen to be fronds of 

 crystalline growth — wonderfully fern-like in appear- 

 ance and sharp in outline (see Figure 2). The drops, 

 which at the beginning of the experiment soon 

 became milky, afterwards remained perfectly clear 

 the whole time they were forming : no separation of 

 opaque calcium carbonate appeared to take place. 



At the end of six months it w as desired to show 

 the stalactite at the Annual Meeting of the Public 

 Schools' Science Masters' Association (January, 1910), 

 so the experiment was stopped and the burette was 



emptied and carefully laid on its side. Then, w ith the 

 point of a knife the " stalactite '" was detached from 

 the burette with the utmost care, and successfully 

 introduced into a glass tube on a cushion of cotton 

 wool, where it still remains. In appearance, it is a 

 delicate, cream-coloured tube of interwoven silky 

 crystals, its whole weight being only one-fifth of a 

 gram. 



The drops of lime-water had fallen from the 

 burette at intervals of about three and a half hours, 

 making a total of eight drops, that is. about three- 

 quarters of a cubic centimetre per day. The drops 

 fell upon a watch glass, where they evaporated to 

 dryness, leaving a slight and apparently amorphous 

 deposit. 



It is interesting to compare the weight of the 

 stalactite given above with the maximum weight of 

 calcium carbonate theoretically obtainable from the 

 amount of lime-water used. Three-quarters of a 

 cubic centimetre a day mean about 137 c.c. in six 

 months (the burette was replenished as required from 

 time to time), and since the solubility of calcium 

 hydroxide in water at the ordinary temperature of a 

 room is '14. the above volume of water will dissolve 

 •19 gram of calcium hydroxide at that temperature 

 if a saturated solution is formed: and "19 gram of 

 calcium hydroxide contains '144 gram of calcium 

 oxide, which is equivalent to '257 gram of calcium 

 carbonate. The stalactite itself weighs "2 gram : 

 the difference being due partly to the fact that some 

 of the stalactite remained adhering to the burette, 

 and partl\- to the fact that some of the lime remained 

 in the drop as it fell : and further, the lime-water in 

 the burette, even if fully saturated at the start, did 

 not remain so, but there was always a certain 

 amount of amorphous calcium carbonate precipitated 

 from the solution, as ma\- be seen at the bottom of 

 the burette in the first photograph. The volume of 

 carbonic acid gas required to form the calcium 

 carbonate of which the stalactite is composed would 

 be contained in about one hundred and thirty-three 

 litres of ordinary air. It might be noted here that 

 the stalactite grew in a room which was onh- 

 occasionally used, and for only short periods, so that 

 the percentage of carbonic acid gas in the air would 

 correspond pretty closely with the normal value. 



So much for the facts : how do they compare with 

 the generalh- accepted theor\- of the formation of 

 stalactites, viz.. that they are invariably produced by 

 the deposition of calcium carbonate from a solution 

 of bicarbonate of calcium ? Here we have an 

 obviously stalactitic growth formed by the dropping 

 of a solution not of bicarbonate of calcium but by 

 one of lime, so that an alternative method of 

 formation seems possible. Do the conditions 

 necessary for this alternative method ever obtain 

 naturally ? Is lime-water ever dropping through the 



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