858 



THE POPULAR SCIENCE MONTHLY. 



with mean temperatures of 77"5 and I'l'V. 

 These figures give a variation of less than 

 6 in a year, and to this limited range is 

 ascribed the debilitating nature of the cli- 

 mate. The mean pressure of the barometer 

 for four years differed but a thousandth of an 

 inch from that indicated at the equator. The 

 coast of the mainland of Africa, Dr. Robb 

 says, is undoubtedly prejudicial to health, 

 and both Europeans and natives of India 

 who pass any considerable time there suffer 

 severely from fever of a bad remittent 

 type, and from dysentery. All seasons are 

 bad, but some are better than others, and 

 travelers going into the interior are usually 

 advised to leave the coast-region before the 

 heavy rains begin to fall. The seeds of dis- 

 ease are often sown by even a short resi- 

 dence on the coast, and the traveler dies 

 before he has advanced many marches into 

 the interior. Travelers, therefore, should 

 always make a careful and quick march 

 across the unhealthy belt of country along 

 the coast, and pitch their camps in the 

 higher and drier districts beyond; and, if 

 they have to linger on the coast, they should 

 take care to pass their nights in the safest 

 places they can find. 



Application of Cold in Industrial Chem- 

 istry. Heat, of temperatures above the 

 freezing-point of water, has long been 

 known and used as one of the most power- 

 ful agents for producing the chemical oper- 

 ations desired by manufacturers. Heat of 

 temperatures below the freezing-point, or 

 cold, as it is commonly called, has been less 

 generally employed, and enjoys less recog- 

 nition as a force capable of practical appli- 

 cation for production. It has been lately 

 made to aid in the manufacture of Glau- 

 ber's salt at some French works with such 

 success as to suggest that its more general 

 application is possible in other directions. 

 Alum and copperas were formerly made 

 from the pyretic shales of Rheims and 

 Picardy, but the product from these sources 

 has been driven from the market by the 

 competition of other alums. A new pro- 

 cess has been devised by M. Georges Four- 

 nier, of Paris, under which the lye from the 

 oxidized shales, containing all of the alu- 

 minum sulphate and a portion of iron sul- 

 phate after a considerable part of the cop- 



peras has been deposited, is mixed with 

 common salt in such proportion that there 

 shall be sodium enough to combine with all 

 the sulphuric acid, and chlorine enough to 

 take up all the aluminum and iron. The 

 mixed solution is then exposed to a temper- 

 ature of from 3 to 5 below the freezing- 

 point, at which the sulphate of soda is 

 almost insoluble. That substance is depos- 

 ited in the ordinary form of Glauber's salts 

 as a fine crystalline sediment, while the 

 aluminum and iron remain in solution as 

 chlorides. The "mother-liquor,'' or lye, is 

 then run off, and the deposit is washed in 

 brine cooled down to the freezing-point. 

 After it is dried, it is fit for any purpose 

 to which Glauber's salt is applicable. The 

 mother-liquid which has been run off may 

 be made into a chloride of aluminum, which 

 is valuable for disinfecting purposes. A 

 pure chloride of aluminum, suitable for use 

 in dyeing, and for the destruction of the 

 vegetable matter which is mingled with 

 wool, may be prepared from cake-alum by a 

 similar cold process. The results of the 

 operation are, as before, a deposit of Glau- 

 ber's salt and a solution of chloride of 

 aluminum, but the latter substance is free 

 from the admixture of iron. Another 

 French inventor, by exposing the lyes of 

 the " sal mixte " of the salt-works of the 

 Mediterranean coast, consisting of common 

 salt and sulphate of magnesia, to a temper- 

 ature of about 11 below the freezing-point, 

 obtains Glauber's salt in deposit with a solu- 

 tion of the chloride of magnesium, a sub- 

 stance largely used for weighting textile fab- 

 rics. 



Fertility of Hybrids. Mr. Darwin, in 

 his " Origin of Species," has mentioned a 

 case on the authority of Mr. Eyton, in which 

 hybrids from the common goose and the 

 Chinese goose were as fertile as among them- 

 selves. He has now reported in " Nature " 

 concerning his success in raising birds from 

 the eggs of a brother and sister from the same 

 hatch of hybrids of these two species. Two 

 trials were made : three birds were hatched 

 from the first set of eggs, two others were 

 fully formed but did not succeed in break- 

 ing through the shell, and the remaining 

 e.vo-s W ere unfertilized. From the second 

 lot of eggs two birds were hatched. The 



