June 1, 1896.] 



KNOWLEDGE, 



lil 



Now, this light- giving property of thorium is just 

 bringing out this rare metal from the complete oblivion in 

 which it has lain for nearly seventy years. Whilst we are 

 writmg these few lines search is being made in many 

 parts of the world for stones, rocks, or sands which may 

 perchance contain a certain quantity of this now precious 

 substance, hitherto a mere useless chemical curiosity. 



It has been found out, indeed, that of all the metallic 

 oxides which have been tried on the so-dilled " hoods '' or 

 "mantles" that are placed around gas-flames in order 

 to increase the light, thoria is by far the finest ; and of 

 recent years the manufacturers of these "mantles" for the 

 incandescent gas-burners have created a brisk demand for 

 thoria. 



The consequence of all this is that, at various times 

 during the last two or three years, a pound u-eiijlit of this 

 hitherto useless substance, thoria, has been freely sold at , 

 forty-five to fifty pounds sterling. 



The incandescent light yielded by the " mantles " of ! 

 thoria are enabling the street gas to rival the more 

 expensive electric light ; and employment in new fields is 

 already being found for thousands of hands, thanks to the 

 discovery, about seventy years ago, of a new substance, 

 apparently of very slight interest, and long considered to 

 be absolutely useless. 



The minerals thorite, orangite, and pyrochlore, which 

 all contain a large amount of thoria, are still very rare 

 and expensive ; but monazite has been found of late years 

 in various parts of the world, and seems more plentiful, 

 and as it generally contains about eighteen per cent, of 

 thoria, it now forms the centre of a new and rising 

 industry. 



However, this mineral, monazite, is by no means common. 

 It is rather heavy, weighing about five times its own bulk 

 of water. In several regions of the United States and 

 Canada, principally near Quebec and in North and South 

 Carolina, it is met with in the sand and gravel which 

 form the bed of small streams, the richest deposits 

 being usually found near the head waters, among 

 the detritus of gneiss rock and schists, where it is 

 associated with several other minerals. In such 

 localities it is either seen in pure crystals — ranging 

 in colour from yellow to brown and yellowish 

 green — sometimes as large as a grain of wheat 

 or even larger, or as " monazite sand," in which 

 minute crystals of the mineral are difi'used or 

 mixed with much ordinary sand and other worth- 

 less material. The principal district is North 

 Carolina, the sands of which yield from two to 

 four per cent, of monazite crystals. Similar 

 sands are now being shipped from the coast of 

 Brazil, which yield from one and a quarter to 

 seven and a half per cent, of monazite. Some 

 monazite sand also comes from Quebec. On the southern 

 coast of Bahia it is found on a sandy beach of enormous 

 extent, and is now being shovelled up from this beach 

 into small vessels of some four hundred to five hundred 

 tons and of light draught, and shipped to England or 

 Hamburg. Norway is also supplying a certain quantity 

 of the minerals thorite and orangite, whicli are very rich 

 in thoria. About one ton weight per annum of these 

 thorium minerals, representing seven thousand pounds 

 worth of thoria, is the present output from the South of 

 Norway. 



Soon after the introduction of (he new incandescent 

 gas burners the demand for minerals containing thoria 

 inerer.sed to a considerable extent. Tlie first oftered were 

 the Norwegian thorite and orangite ores, which contained 

 from forty to sixty-two per cent, of the rare oxide. At first 



the price paid for pure oxide of thorium was as higo as 

 fifty-three pounds for one pound weight avoirdupois ; but it 

 has since oscillated very much, and has sometimes been as 

 low as seven pounds per pound, according as the output is 

 more or less plentiful. 



We have, perhaps, said enough to show that a new and 

 highly interesting branch of industry has arisen in a most 

 unexpected manner, from a chemical discovery which, at 

 the time it was made, and ever since, has been generally 

 regarded as one of the most useless and least promising, 

 from a commercial point of view, in the whole annals 

 of scientific research. 



SERTULARIAN POLYPIDOMS; OR "HORNY 

 CORALLINES." 



By P. L. Addison, F.G.S., Assoc.M. Inst.C.E. 



THE heaps of tangle which lie at high-water mark 

 along our coasts contain a variety of objects it 

 would be almost impossible to catalogue, but 

 which, with certain exceptions — such as cabbage 

 stalks, old boots, and the like— are all of more or 

 less interest to the naturalist. Tlie principal mass of the 

 tangle consists of a great variety of seaweeds, ranging from 

 the thick stems of the common bladder-wrack to the most 

 delicate fronds of the Uriijiihsia and Chulophora. Clusters 

 of egg-cases of the whelk, like balls of sea foam that have 

 been petrified, egg-cases of the skate, defunct starfish, 

 sea-urchins, and small crabs are among the first objects 

 which arrest attention. All these have an attraction 

 of their own, but it is to the remains of a much less 

 conspicuous class of marine animals that we now wish to 

 draw the reader's attention. These are the polypidoms 

 or polyparies of the zoophyte family Sertulariida : small, 

 graceful, branching, tree-like objects, which are usuaUy 



FlO. 1 — Sertularia gracilis. 



found in the tangle in great variety after a storm. They 

 are often mistaken for seaweed by the casual observer, 

 and were formerly considered to belong to the vegetable 

 world. They are frequently called "corallines," or "horny 

 corallines " ; but the popular names must not allow them 

 to be in any way associated with the common coralline 

 (Coraltina oilicin'ilis), which is a true but very remarkable 

 form of marine alga. 



With the help of a small pocket magnifier it may easily 

 be seen that along each side of the stem and branches of 

 the polypidom are arranged minute cup-like projections, 

 placed alternately, or opposite to each other, according to 

 the species of Sertularia to which they belong. In the 

 allied Plumularia the cups are on one side of the stem 

 and branches only. 



Sertulariau zoophytes are very similar in bodily sti uc- 



