Vol. XXII. No. 12.] 



POPULAE SCIENCE IsTEWS. 



177 



Practical Cbemiatrp anil t&c 3[rts. 



THE RARE METALS. 



Chemists have found about seventj'-one 

 different forms of matter, which they call 

 elements, and are apparently simple forms of 

 matter incapable of further subdivision. We 

 say about seventy-one different forms, because 

 some of these so-called elements have been 

 but little studied, and resemble each other so 

 closely that they may be proved to be identical, 

 or to be mixtures of still simpler forms. The 

 question of the true nature of the elements has 

 been frequentlj' discussed in these columns, 

 but is not connected with the present subject. 



Of these seventy-one elements, fiftj^-six are 

 metals and fifteen metalloids. It is rather 

 difficult to exactly- define a metal ; but their 

 general appearance is familiar to every one, 

 and a special article upon this question 

 will be found in the Science News for 

 March, 1887. Only about thirty ele- 

 ments are at all common, and not 

 more than twenty are met with in 

 daily life. Sixteen of these ai'e of a 

 metallic nature, leaving forty different 

 metals which are rarely seen outside 

 of a laboratorj- or mineralogical cabi- 

 net, but which in their chemical rela- 

 tions are of considerable interest. 



Beginning with that group of ele- 

 ments containing the familiar sub- 

 stances sodium and potassium, we find 

 three other metals closely allied to 

 them, — lithium, rubidium, and cae- 

 sium. Lithium is more abundant than 

 the other two, and is found in con- 

 siderable quantity in many mineral- 

 spring waters, including those at Sara- 

 toga. 



It is the lightest solid element known, 

 having a specific gravity of 0.59, or 

 about one-half that of water. 



Caesium and rubidium were also first 

 discovered in mineral water by Bunsen and Kir- 

 choff in 18G0. There were only two or three 

 grains of the metals to a ton of water, and 

 their detection would have been impossible, 

 except for the spectroscope, which showed 

 the blue line of caesium and the red one of 

 rubidium, when even this minute quantity was 

 present. The metals themselves present no 

 especial peculiarity of appearance, and could 

 hardly be distinguished by sight from a piece 

 of sodium or potassium. 



In the calcium and magnesium group, we 

 find barium and strontium, which, while not 

 very rare, have but few practical uses. Stron- 

 tium is largely used for making red fire, 

 wliile barium gives a green hue to the flame. 

 Cadmium is a metal resembling zinc, and is 

 only important as being a constituent of the 

 fusible alloys used for safety-plugs in steam- 

 boilers, automatic sprinklers, etc. 



Aluminium is no longer an uncommon metal ; 

 but there is a long list of similar metals which 

 are quite rare, and of little or no practical 

 importance. They resemble each other very 



closely, and it is bj' no means certain that 

 they are all distinct elements. The elements 

 yttrium, erbium, terbium, phillipium, ytter- 

 bium, and samarium are very slightly dif- 

 ferentiated, and are compared by Dr. Crookes 

 to the refuse of the universe " heaped away 

 in some cosmical lumber-room ; " while the 

 deceptive nature of another supposed element 

 is expressed by its name, decipium. Gallium 

 and germanium were discovered by French 

 and German chemists respectivel}' ; while 

 scandium is remarkable, as agreeing in its 

 properties with a theoretical element which 

 was required to fill a vacant place in the 

 " periodic system " of the elements, but was 

 until quite recently unknown. 



Glucinium is found in the emerald and beryl, 

 and some of its salts have a sweetish taste. 

 Zirconium is the base of the rare minerals 

 zircon and hyacinth, and thorium is remark- 



able for its specific gravity (9.4) and the 

 highest atomic weight (232) of any element. 

 Cerium is used to a small extent in medicine, 

 and lanthanum and didymium closely resemble 

 it. The name "lanthanum" means "to lie 

 concealed," and was given on account of 

 the difficulty of its detection ; and didym- 

 ium closely resembles it, as the meaning 

 (" twinned ") of its name implies. Indium 

 was discovered by the blue line which it gives 

 in the spectroscope, and uranium is only used 

 for the purpose of coloring glass and por- 

 celain. 



Thallium is a metal resembling lead, and 

 gives a green line in the spectroscope, bj' 

 which it was first discovered. Titanium is 

 related to tin, and is an undesirable constituent 

 of certain iron ores. It also imparts a yellow 

 color to glass and porcelain. Tungsten is a 

 valuable addition to steel ; and tungstate of 

 soda, applied to wood or clothing, renders them 

 uninflammable. Niobium and tantalum resem- 

 ble each other very closely, but are of little 

 importance. 



INIolybdenum belongs to the iron group, 

 which also includes nickel, cobalt, and man- 

 ganese. Vanadium is allied to antimony and 

 nitrogen, and has been found to possess a re- 

 markable 'oxidizing power. It is extensively 

 used for the production of aniline black in dye- 

 ing and calico-printing establishments. About 

 one per cent of vanadate of ammonia added 

 to an infusion of nut-galls makes a very supe- 

 rior black ink, which, however, will partially 

 fade in time. 



We come, last, to the rare metals of the 

 platinum group, of which iridium is the most 

 useful, as, on account of its excessive hardness, 

 it is used for the points of gold pens and 

 stylographs, the knife-edges of balances, etc. 

 Osmium is one of the most poisonous sub- 

 stances known ; while palladium is remarkable 

 for the readiness with which it combines with 

 hjdrogen, apparently forming an alloy, and 

 indicating the metallic nature of that 

 gas. It has latelj* been used as a sub- 

 stitute for steel in certain parts of 

 watches, to avoid the effect of mag- 

 netism on the works. Ruthenium and 

 rhodium are of no special interest. 



There are probably many other 

 metals in existence which remain to be 

 discovered. We are familiar with but 

 a small portion of the crust of the 

 earth, and know nothing of what there 

 may be at a little distance below it. 

 In the " periodic sj'stem " of the ele- 

 ments there are several gaps yet re- 

 maining to be filled, and elements pos- 

 sessing the required properties may 

 some time be discovered. Whatever 

 new elements may be found, will un- 

 doubtedly occur in ver}' small quan- 

 tities ; but at present there seems to 

 be no limitation to the number of 

 "rare metals" read3' to indicate their 

 presence in the spectroscope, beakers, 

 or crucibles of the chemist who pa- 

 tiently searches for them. 



CARICATURE PHOTOGRAPHS. 



It is an easy matter for the photographic 

 amateur to produce distorted portraits, similar 

 to those represented in the engraving, with an 

 ordinary camera. The method as described 

 in La Nature is as follows : — 



A full-length picture is taken in the usual 

 way, against a perfectly plain background, and 

 without any accessories. From this negative 

 a positive on glass is made by placing it in a 

 printing-frame against a sensitive glass plate, 

 and exposing to the light of a lamp or candle 

 for a few seconds. The positive transparency 

 is developed and finished, and placed before 

 the camera so that the light passes through it, 

 but inclined at an angle to the camera, either 

 lengthwise or sidewise according as the image 

 is to be shortened or lengthened, and a second 

 negative taken which will give the distorted 

 figures shown in the engraving. To obtain 

 the best results, the lens used in taking the 

 distorted picture must be of very short focus, 



