May 12, 1882.] 



KNOWLEDGE 



583 



melancholy fate of Tennyson's Queen of the May, if, on 

 one of our modem May -days, she — 



." Danced about th:; M iyp;lo, a:id in tlio hazel coi'se, 



Till Charles's wain came out above the tall white chimney-tops." 



Someone should have explained to the merrymakers that 

 the sun had not yet attained a mid-day altitude which 

 could justify these gambols in the hazel copse — that., in 

 fact, they ■would probably result in what Sidney Smith 

 calls " our British constitutional coughs, sore throats, and 

 swelled faces.'" His advice would have been scouted, no 

 doubt, and he would have been looked upon as a bore and 

 a nuisance ; but he would have been right all the same. 

 Indeed, speaking seriously, in these days, when many, 

 especially the younger folks, look back longingly on old 

 customs, and occasionally try to revive them, it may some- 

 times be well to inquire even into such dull, dry details as 

 the eflects of the change of style in modifying the relations 

 of dates and seasons. 



CRYSTALS. * 



By William Jagg, F.C.S., Assoc. Ikst. Ciiem. 



THE object of this and the succeeding papers of this 

 series is to place before the readers of Knowledge an 

 account of the Chemistry and Chemical Physics of different 

 subjects of general interest in as plain and interesting a 

 manner as is possible to the writer. It must not be sup- 

 posed, however, that the result will be a regular and suc- 

 cinct chemical treatise ; those requiring such can find them 

 in abundance, and of all prices and qualities. The writer 

 would rather treat his science so that they who run may 

 read, appealing, he hopes, to those who, though busy in the 

 shop, the field, the mart, have not ceased to take an in- 

 terest in Science for her own sake. A very clear and 

 interesting account of the properties of matter in the 

 gaseous state, which appeared in one of the earlier numbers 

 of Knowledge, led to an account of its behaviour in the 

 solid condition being chosen as the subject of this intro- 

 ductory paper. 



Let us start with the inquiry, " What is a crystal ? " and 

 probably at the outset we shall be met with an answer 

 which, curiously enough, selects as its typical example the 

 very substance of all substances that a chemist instances 

 as the tj-pe of non-crystallised bodies. Nine persons out 

 of ten will tell us, in response to our query, " A crystal is 

 anything which is verj- clear, like gJais." Go to the chemist 

 or geologist and ask him whether a piece of that black, 

 shiny lava poured out of a volcano is crystalline, and he 

 will say; " No, it is a specimen of the glassy (vitreous) type 

 of rock." Here, then, is one point at which the chemist at 

 once joins issue with the popular idea. Let us in the next 

 place ask him for his definition of a crystal, and we learn 

 that almost every solid substance known has a tendency 

 to arrange itself in a definite geometrical form, and 

 that it is then said to be crystallised. This change of 

 bodies from the condition in which their particles are 

 arranged irregularly, to that in which each occupies a 

 stated position, forming part of one haiTuouious whole, 

 is frequently accompanied by remarkable changes in 

 the appearance and properties of the suljstance. Carbon, 

 known to every one in the humble and familiar guise of 

 charcoal, crystallises and becomes a diamond ; and further, 

 this depends on its particles arranging themselves so as to 

 form the figure known as an octahedron ; witii a change 

 of the conditions, the same elementary substance varies tlie 

 crystallised form it assumes, and instead of the hard and 

 brilliant gem, we have produced six-sided plates of soft 



and metallic-looking graphite, or black lead. Nature 

 carries on within her laboratory these wonderful changes, 

 giving us little or no idea of what she is doing unless we 

 watch and question her closely ; her secrets are, however, 

 readily revealed to him who questions aright Owing to 

 the value and beauty of the diamond, eftbrts have been 

 made, from the days of the alchemist downwards, to obtain 

 it artificially; these eflbrts have, however, met with but 

 little reward. Nature has one element of success in her ex- 

 periments which we can never have, and that is time. The 

 diamond, sparkling in a lady's ring, no Viigger than a pea, 

 has, in all probability, taken for its growth not days or 

 months, but years, reckoned by thousands, or perhaps 

 hundreds of thousands ! How, then, shall we imitate her 1 

 In this particular instance, probably in no way ; but there 

 are fortunately other substances knoiivn which crystallise 

 more readily, and with these we may hope to have success. 

 Most of the metals assume, under certain conditions, a 

 crystalline form, and those particularly which are found 

 native occur frequently as crystals. The Latrobe nugget, 

 at present in the Natural History Museum, is a magnifi- 

 cent instance of crystals of gold ; it consists of natural 

 golden cubes, welded, as it were, together in one mass. 

 Among the metals, bismuth is remarkable for its ten- 

 dency to crystallise, and by following the direc- 

 tions given, a ci-ystalline mass of bismuth is readily 

 obtained. Take about a quarter of a pound of the 

 commercial metal and melt it either in a small clean 

 iron ladle or over a Bunsen lamp in a porcelain crucible ; 

 when quite melted, set the ladle or crucible on a cold 

 metal surface. Let it remain perfectly still, and watch the 

 bismuth carefully, until it is seen to solidify round the 

 edges, then quickly pour out the metal still remaining 

 liquid, and you have the whole of the interior lined with 

 more or less perfect cubical crystals of bismuth. There is 

 one striking peculiarity about these crystals, however. 

 They are but skeleton crystals ; the lines forming the 

 edges of the cubes are there, but there is a depression in 

 each face of the crystal evidently not as yet filled up. The 

 growth of the crystal was arrested by pouring out the still 

 liquid metal, and there we have not only shown us the 

 shape of bismuth crystals, but also the mamier in which 

 the crystal grows. 



For purposes of comparison, try now to make sulphur 

 crystals. To do this, melt down roll sulphur in the ladle 

 or crucible, using, however, a very gentle heat, and not 

 pi'oloiiging it beyond the point at which the whole of the 

 sulphur is melted ; allow to cool in the same manner as 

 with bismuth, wait until a crust has formed over the sur- 

 face, and then immediately bore two holes through with a 

 red-hot wire, the one for the liquid sulphur to run out, and 

 the other to admit air. Pour out the sulphur still remain- 

 ing liquid, and cut carefully round the upper crust with a 

 penknife, remove it, and the whole of the interior is inter- 

 laced with delicate needle-shaped, amber-like, crystals of 

 sulphur. Here, then, are two substances, of widely dif- 

 ferent appearance and properties, both possessing in com- 

 mon this property of crystallising, but with each there is a 

 detinite shape. Further experiment and observation teach 

 us that the form of a crystal is as characteristic of a body 

 as any other property it possesses. In the next paper the 

 writer pui-poses to give further directions for the prepara- 

 tion of crystals, and hopes to add sketches of crystals 

 as viewed by the microscope. 



In an early number, probably the next, an important series of 

 papers by Miss Amelia B. Edwards, the eminent authoress and 

 Egyptologist, on the question, "Was Barneses II. the Oppressor of 

 the Hebrews?" will be commenced. 



