ilAY 19, 1882.] 



KNOWLEDGE 



601 



1790 and 1791 was a warm month throughout, May in 

 1792 was cold and bleak. Certainly there is no evidence 

 here of extreme regularity. 



I have already pointed out (see last number) that the 

 praises bestowed by the poets of the sixteenth and seven- 

 teenth centuries upon the month of May do not relate to 

 tlie thirty-one days forming the May of our present year, 

 but to those which now fall between May 11 and June 11. 

 The May-day of those times fell, strangely enough, at the 

 \erv coldest part of what may be called the average cold 

 week of May, but the month of ilay, as a whole, was 

 then much warmer on the average than our present May, 

 Jind well deserved Dryden's warm description : — 



For thee, sweet month, the fjroves green liTrics wear, 

 If not the first the fairest of the Tear; 

 Tor thee the Graces lead the daiicinjr honrs, 

 And Nature's ready pencil paints the tlow'rs. 

 Xhe sprightly May commands our youth to keep 

 The vi^ls of her night, and breaks their sleep ; 

 Kach gentle breast with kindly warmth she moves, 

 Inspires new flames, revives extinguished loves. 



It is only when the average temperatures of the first 

 ■fourteen days of May are considered, that we find the now 

 jirevalent belief in a " cold week in May " fully justified. 

 The curve of temperature for the year from the ob- 

 servations of the last half century, shows, as already men- 

 tioned, a decided depression at the part corresponding to 

 tlie second week in Jlay, thougli it is to be noticed that it 

 <lips down quite us decidedly at the part corresponding to 

 the second week in April. It appears to me that when we 

 cooibine the ascertained fact that there is on the average a 

 fall of temperature at this part of ^lay, with the equally 

 <-ert;\in fact that there is no regularity in the recurrence of 

 the cold week, we must regard as extremely improbable 

 the theory which attributes the peculiarity to a cosmical 

 <ause. This theory was thus placidly presented some time 

 .•i_'o by M. de Fonvielle as a known truth : — 



'• The chilliness is due to the fact that the earth passes 

 4i'liind a ring of asteroids, which absorb a portion of the 

 ■.iin's warmth, due to us while it remains above the horizon. 

 The temperature will not resume its ascensional movement 

 vuitil the annual rotation shall have carried our sfihere from 

 the shadow of the multitude of the small planets which is 

 always projected on the same point of our orbit" 



>'e.Kt week, I shall point out a few objections to this 

 theory. 



I'oisoNOUS Crayons. — A little girl, o-t. two-and-a-half years, 

 i-occntly died at Brockley from the effects produced in part by 

 .sucking poisonous crayons. At the in<iuest held on the body, the 

 trade.sman from whom the things hud been purchased disclaimed all 

 knowledge of their injurious properties, and said that he sold them 

 in considerable quantities in penny boxes. I'nst-mortem examina- 

 tion, however, revealed that the brain and stomach alone of all the 

 ot^ns were in an unhealtliy condition. Tiie stomach was much in- 

 flamed, and perforations of its coats occurred in two places, while 

 the left side of the brain was distended with fluid. There was 

 eiidence that the child had sustained a fall, and to this it was 

 sought in part to attribute the death ; but information concerning 

 the accident was incomplete and unsatisfactory, although the jury, by 

 their verdict, credited it in part with the fatal result. Analysis of the 

 crayons conclusively proved that they all contained poisonous 

 material, and there can be little donbt they were chiefly to blame 

 fuo: the death. One of the crayons, a pink one, contained inore than 

 fifty per cent, of its weight of white leail, and as the unfortunate 

 little victim lingered for three weeks in much suffering, it ought to 

 be possible to ascertain how far this substance influenced her con- 

 <iition. The newspaper reports give ver.- insufficient details of the 

 ease, of which, however. Dr. Kavanagh, the medical attendant, may 

 |iossibly provide more comprehensive notes. The case is an instruc- 

 tive one, as showing the need for sweeping measures of reform in 

 connection with the indiscriminate sale of poisonous materials of all 

 sorts by general shopkeepers ; and in this way it may excite useful 

 <lirenssion. — Hedical Press. 



CRYSTALS. 



By William Jaco, F.C.S., Assoc. Is.st. Ciiem. 

 No. II. 



IN the last paper on this subject directions were given 

 for the preparation of crystals of bismuth and sulphur, 

 in both cases liy the solidification of the fu.sed .substance. 

 Before leaving the ciystallisation of metals, reference should 

 be made to those experiments in which metals are dis- 

 placed from a solution of their .salts by some other element. 

 The well-known '• lead tree " is a type of such changes ; 

 its formation depends on the fact that zinc is a more activi- 

 element, chemicallj-, than lead ; hence, if zinc be introduced 

 into a solution of a compound of leatl with an acid, the lead 

 is "displaced,"' and its former position usurped by the zinc. 

 The lead is deposited in the metallic state, and under 

 favourable conditions assumes a beautiful crystalline 

 form. The experiment of making a lead tree may bo 

 performed with a tiiiniinnm of apparatus and experience 

 of chemical manipulation. An ordinary pickle bottle, or 

 other vessel of clear glass and similar shape being obtained, 

 fill it with a solution of lead acetate (sugar of lead). About 

 an ounce of the acetate will be sufficient for a bottle of the 

 size mentioned : if dissolved in spring water, a slight sedi- 

 ment will be formed — this, however, if allowed to subside, 

 will not interfere with the experiment. Distilled or even 

 rain-water is preferable for making chemical solutions. 

 Next a fragment of clean zinc, about the size of a small 

 walnut, must be procured, the more irregular the better ; 

 suspend this by a piece of string, the end of which 

 passes through a hole bored in the oork of the bottle 

 containing the acetate. Put the zinc in the bottle, 

 cork it up, and so arrange the length of the string 

 that the zinc is just beneath the neck ; fasten it in this 

 position, and set the whole arrangement where it will not 

 be disturbed. In a short time crystals of lead will be 

 seen to deposit themselves on the zinc, and soon it will be 

 covered with a tree-like growth of crystals. If left per- 

 fectly still, it remains a long tune before the mass drops 

 off. With this anil other similar experiments, one half the 

 pleasure consists in watching and studying the crystal 

 growth for one's self.* Silver, which is in many respects 

 a metal closely allied to lead, may also be made tlie subject 

 of interesting experiments on crystallisation ; the so-called 

 Arbor Diana' is produced by placing a globule of mercury 

 in a solution of nitrate of silver; a growth ensues of long 

 thin crystals of an amalgam of silver ; these, in addition 

 to their beauty of shape, possess that magnificent lustre 

 which causes mercury and silver to be almo.st unrivalled 

 among the metals. 



Those who possess a microscope will find a few prepared 

 specimens of crystals a valuable addition to their stock of 

 slides. Not only are they of great interest, but as an in- 

 troduction to microscopic analysis and microscopic study of 

 rocks, the systematic student will find them worthy of 

 special study. It has been previou.^ly stated that the 

 crystalline form of many substances is one of their most 

 characteristic properties ; and as in the detection of poison 

 and other important cases there is often a trace merely of 

 the substance to be obtained, a microscopic examination is 

 of great importance ; it has, too, this further merit, that 

 the substance is afterwards available for other chemical 

 tests. 



The preparation of such slides is very simple. In the 

 first place the glass slips must be perfectly clean and free 

 from grease ; it is well to wash them in a solution of soda, 



• It should be stitcd thac lead acetate is a poisonous salt. lu 

 all cases chemicals s:iouId b? kept clearly labelled and locked up. 



