180 



CHEMISTRY. 



has also extended his observations to the dis- 

 sociation of the elements of carbonic acid by 

 means of heat. 



Deposit of Camphor toward the Light. It 

 has been generally stated in books of chemistry 

 that camphor vapor has a tendency to be de- 

 posited toward the light ; that is, if a bottle con- 

 taining camphor be exposed to sunlight, the 

 camphor will be deposited in crystals against 

 that side of the bottle which is turned toward 

 the light. Mr. 0. Tomlinson's experiments have 

 led him to conclude that heat'is the real agency 

 concerned in determining the phenomenon thus 

 observed. He exposed a great number of bottles 

 of camphor to light under different circum- 

 stances (as, for intance, when immersed in 

 water), and found that no deposit was formed 

 under those conditions that prevented a radia- 

 tion of heat. 



His theory is to the effect that, in all cases 

 in which deposits are produced in preference 

 upon one side of a containing vessel, as of such 

 materials as camphor, naphthaline, iodine, 

 mercury, water, &c., from the state of vapor, 

 this result is determined in accordance with 

 two well-known laws: 1, there has been a ra- 

 diation of heat to greater extent from that sur- 

 face, rendering it colder than the vapor in its 

 vicinity ; and, 2, a condensation of vapor then 

 takes place by contact with the colder surface. 

 A like result is obtained with some salts in 

 solution. 



VI. THEORETICAL CHEMISTRY. Numerical 

 Relations of the Alkali-Metal Equivalents. M. 

 Dumas remarks that, among the alkali-metals, 

 thallium is (so far as yet known) the last term 

 of a scale of numerical relations in which lithium 

 is the first, and in which the equivalents of the 

 others mark so many different degrees. Thus, 

 taking Li as 7, and correcting Dumas' list and 

 ratio (in this single particular) with Profs. 

 Johnson and Allen's result for caesium, we have 

 the following scale : 



Element*. Eqniralentt. 



Lithium . 1 



Sodium 28 



Pottissi am 39 



Enbidinm 85 



Cesium 188 



Thallium 204 



Now, between certain terms of this series 

 the following striking relations are to be dis- 

 covered : 



1. Li, Na, and K form a triad, the equiva- 

 lent of the middle term of which is exactly the 



Y J.QQ 

 mean of those of the other two, thus, 



= 23. 



2. K, Rb, and Cs appear to form a second 

 triad, the equivalent of its middle term being 

 almost exactly the mean of those of the other 



A , 39 + 183 

 two; thus, ^ = B6. 



8. Addition of double the weight of Na to 

 that of K, gives precisely the weight of Rb ; 

 thus, 23x2 + 39 = 85. 



4. Addition of double the weight of Na to 



the weight of Rb, gives approximately the 

 weight of Cs; thus, 23x2 + 85 = 131. 



6. Addition of double the weight of Na to 

 4 times that of K, gives approximately the 

 weight of Tl ; thus, 23 x 2 + (39 x 4) = 202. 



These relations, Dumas believes, must at- 

 tract the attention of chemists ; and without 

 attributing to them a value that the actual num- 

 bers would not justify, they show the interest 

 which attaches to the careful comparison of 

 the equivalents of bodies belonging to the same 

 family. 



[The analogies above shown, if they have 

 any real value, would appear to suggest a 

 doubt whether the equivalents of some of the 

 elements here considered have yet been with 

 entire correctness determined.] 



VII. APPLICATIONS OF CHEMISTRY. For cer- 

 tain applications of chemical facts and princi- 

 ples, the reader is referred to the subject of 

 ILLUMINATION, and some others of the heads 

 previously mentioned in this article. 



Coloring Articles of Copper and Brass. Mr. 

 J. Hunt, of Birmingham, England, coats arti- 

 cles of copper and brass with platinum, by im- 

 mersing them in a weak solution of the bichro- 

 mate of that element, heated to the boiling 

 point, and then by the galvanic battery in the 

 usual method causing the deposit of a thin film 

 of the metal over their surfaces. The effect is 

 to impart to the articles so treated a bright 

 steel color, which, when the articles before im- 

 mersion are burnished, is of a beautiful bluish 

 cast. 



Bronzing Cast Iron. The pure copper which 

 is deposited by a galvanic battery "has been 

 found to be peculiarly adapted to the coating 

 of cast-iron figures exposed to the weather. 

 This copper is mixed in a state of powder with 

 oil, and is then laid on with the brush, as a 

 paint. The iron balcony decorating the facade 

 of the Theatre Francais, in Paris, is thus 

 bronzed. 



New Uses of Aluminium Bronze. An ac- 

 count of the composition and properties, and 

 of certain uses, of aluminium bronze, was given 

 in the preceding volume. As the bronze is 

 very ductile, and well suited to the processes 

 of rolling and hammering through which steel 

 and gold require to be passed in the making 

 of pens, Mr. R. Pinkney, of London, proposes to 

 substitute it for those metals in the manufac- 

 ture of pens. He states that the alloy of which 

 the aluminium amounts to 95 per cent, has a 

 fine gold color ; while that in which the cop- 

 per forms 7^ per cent., is of a beautiful green. 



Mr. J. Erwood, also of London, has patent- 

 ed the manufacture of^ bronze powders and 

 leaf from the aluminium bronze, and which 

 are intended to take the place of the powders 

 and Dutch-metal leaf in common use, for 

 application to paper-hangings, gildings, &c. 

 Copper 90 parts to 10 parts of aluminium are 

 said to produce a bronze of a fine yellow color. 

 This is rolled, annealed, and beaten to the 

 thinness of foil or leaf; and in this form it can 



