Page:Encyclopædia Britannica, Ninth Edition, v. 5.djvu/544

Rh 532 CHEMISTRY [ALUMINIUM Pb(C 2 H 5 ) 4, the existence of which affords conclusive evi dence that lead may function as a tetrad element, is obtained by the action of zinc ethyl on the chloride PbCl 2 C?Pb 2 Cl 4 ). The hydroxide, Pb(C 2 H 5 ) 3 .OH, is powerfully basic. Compounds of thallium with hydrocarbon radicles only have not yet been obtained ; a thallium diethylchloride, Tl(C,H 6 ) 2 Cl, is known, however. It is a crystalline body of remarkable stability, and is readily converted into the hydroxide, T1(C 2 H.) 2 .OH, which is also crystalline and very soluble in water ; the solution is strongly alkaline, nevertheless the hydroxide does not exhibit the slightest tendency to attract carbon dioxide, although it readily forms salts with other acids. The relation of thallium to lead will be sufficiently evident from the above sketch of the properties of some of the more important compounds of the two elements ; it will be noticed also that thallium has strong points of resemblance with the metals of the alkalies, and that it is in some respects related to mercury. Its relation to the alkali metals is especially indicated by the extreme readi ness with which it is oxidized, by the properties of thallious hydroxide, and by the isomorphism of many thallious compounds with the corresponding potassium and sodium -compounds. Thermochemical investigation entirely con firms these conclusions, as will be evident from the follow ing tables, the heat of neutralization of thallium hydroxide being equal to that of the hydroxides of potassium and sodium, but the affinity of thallium for oxygen being only about equal to that of mercury and copper, and somewhat less than that of lead. The heat of neutralization of thallic hydroxide exceeds that of aluminic hydroxide. Reaction. Units of heat devel oped or absorbed. Remarks. fTl a, 0.... 42,240 i T1 2 0, H0 3,230 TL, O.HoO 45,470 1 Tl, 0,H 56,915 T1 2, 3 , 3H 2 86,010 3f&amp;lt; Tl, Cl 48,580 n, Tl. Br 41,295 1 Tl, I 30,180 I Tl.O.NO, 60,140 {Formation of the salts from the metal, oxygen, and o Tlj,O a ,S0 3 149,900 gaseous nitric peroxide Tl,0, H, Aq 53,760 or sulphur dioxide. 3 T1 2 ,0, Aq 39,160 8 -J2 T1 3 ,0, N 2 5 Aq 66,540 IThe salts are produced from the metal, oxygen, and P3 Tlj, 0, S0 3 Aq 70,290 dilute aqueous solutions o 3 Tl, Cl, Aq 38,480 a Tl, Cl, , Aq. . . 89,000 Tl.Br,, Aq... 56,180 I* Tl, I, , Aq 10,550 T1.0, O a ,3H 2 0... 43,770 (&quot;Tliallions oxide find hydr- Tl(OH), 0,H 2 20,270 1 thallic hydroxide by oxy- Tl(OH)Aq,0 23,425 [ gen and water. /Oxidation of an aqueous 2Tl(OH)Aq, H 2 S0 4 Aq Tl(OH)Aq, HN0 3 Aq.. Tl(OH)Aq, HClAq T10 s H,,3HBrAq Tl(OH)Aq, HClAq Tl(OH)Aq, HBrAq Tl(OH)Aq,HIAq Tl 2 HClAq . 31,130 13,690 13,760 30,570 23,860 27,510 31,610 44 640 ( solution. (The chloride being retained in solution. 1 T1 2 0, 2HBrAq 51,940 1 Trie haloid thallious com- T1 2 0, 2HIAq 60,140 precipitated. T1 2 O, 2HC1 79,280 T1 2 0, 2HBr 91,820 TLO, 2HI 98,560 T1 2 0, Aq - 3,080 T10H, Aq - 3 155 T1N0 3, Aq - 9 970 TLS0 4 , Aq TIC1, Aq - 8,280 -10 100 Reaction. Units of heat developed. Remarks. Pb, 50,300 Pb,Cl 2 82,770 I Formation of the solid, com- Pb, Br 2 64,450 f pounds. Pb,T 2 39,670 PbO,2HCl 56,830 / PbO,2HBr 65,630 PbO, 2HI 69,810 PbO, 2 HClAq.... 22,190 PbO, 2HBrAq... 25,750 The products being entirely PbO,2HIAq 31,390 precipitated. PbO,S0 3 Aq 23,500 PbO, 2 5 Aq 17,770 PbO, 2H01Aq.... 15,390 ) The chloride and bromide being PbO, 2HBrA&amp;lt;i... 15,710 dissolved. PbO, 2C s H 4 2 Aq 15,460 Pb,0, S0 3 Aq.... 73,800 The su]phate being precipitated. Pb, 0, N 2 O 5 Aq.. 68,070 Pb, C1 2, A (I 75,970 Pb,Br 2 , A.i Pb(N0 3 ) 2 ,Aq.... 54,410 - 7,600 PbCl 2 , Aq - 6,800 PbBr 2 , Aq -10,040 BORON ALUMINIUM INDIUM. Name. Symbol At. wt. Sp. gr. At. vol. Electric conduc tivity. Boron B 11 2 6 4-2 Aluminium Al 27-3 2-6 10-5 3376 at 20 C. Indium In 113-4 7-4 15-3 The first of these elements has already been described. Aluminium is related not only to boron but also to silicon among the non-metals, and to magnesium among the metals. Its oxide is one of the most stable known, and, like silicon and boron oxides, cannot be reduced by charcoal alone. The metal is usually obtained by heating the double chloride of sodium and aluminium, 2NaCl,Al 2 Cl G , with sodium. Aluminium is a white malleable metal, nearly resembling zinc in colour and hardness ; it fuses at a lower temperature than silver, but does not volatilize. It is rapidly dissolved by hydrochloric acid, but only slowly acted on by heated nitric and sulphuric acids ; it is readily dissolved by solutions of the alkalies. In a finely-divided state it appears to decompose water almost as easily as mag nesium, but when in mass, even if heated to full redness in steam, it decomposes water but slowly, owing to the formation of a coating of oxide on its surface which protects the metal ; on this account also it may be heated intensely in air with out undergoing more than a superficial oxidation, but in the form of powder it burns brightly when heated to redness in air or oxygen. Aluminium takes fire when heated in chlorine gas, and is converted into the chloride, which is also produced on passing chlorine over an ignited mixture of alumina and charcoal. Aluminium forms only one chloride, the density of which in the state of vapour corresponds with the formula A1 2 CI 6 ; it also forms only a single oxide, A1 2 3. Aluminium chloride is a colourless, crystalline, volatile substance ; it is deliquescent and dissolves readily in water, much heat being developed, forming a strongly acid solution. Aluminium hydroxide, A1 2 (OH) 6, separates as an almost colourless gelatinous precipitate on the addition of alkalies to a solution of an aluminium salt ; it is readily soluble in acids, forming salts such as aluminium sulphate, A1 2 (SO 4 ) 3. Aluminium sulphate is extremely soluble in water ; it is very readily converted into basic salts ; it combines with the sulphates of the alkali metals forming characteristic double salts the so-called alums. Aluminium hydroxide also possesses marked acid properties, being soluble in alkalies, and furnishing salts such as sodium aluminate, Na fj Al 2 6. On ignition alum-i-
 * oxide are converted into
 * Solutions being formed.