4')6 TRANSACTIONS OF THE AMERICAN INSTITUTE. 



would be condensed to a liquid, while the impure gases Trould 

 not be aflected. There appear to be practical difficulties in the 

 Tvay of all application of this method. If it were feasible, it would 

 have an application as a powerful freezing compound, as the solid 

 carbonic acid produces a cold estimated as low as one hundred 

 and eighty degrees below zero of Fahrenheit, and it could be used 

 as a motive power in properly constructed engines. 



Magnesium Light. 



A peculiarity of the light produced by the combustion of magne- 

 sium, IS that colors are not affected by it any more than by the 

 light of the sun. A flower-bed lighted up at night reveals all of 

 the natural colors, the same as in the day-time ; and it has been 

 proposed to use the light to distinguish the shades of color in silk 

 and dyed goods at night, or during cloudy days. Numerous alloys 

 of magnesium have been tried, but none of them with entire suc- 

 cess. It is difficult in melting the metals to prevent the burning 

 up of the magnesium. The alloy with lead burns very well, but 

 the best results have been obtained with zinc. Alloys containing 

 ten, fifteen or twenty per cent, of zinc, are easily drawn into wires 

 and burn regularly, but produce much smoke, and act less power- 

 fully in photography. 



Nitrate of Soda. 



This article of commerce is sometimes called Chili saltpetre; 

 also cubic nitre. It is found in large quantities in Peru. Iquique 

 is the small port on the coast where the vessels can take in their 

 cargoes. The nitrate of soda is brought from a district of country 

 ninety miles in the interior. This district, where the nitrate forms 

 beds mixed with clay, has a circumference of fifty miles, and is 

 called Atacama. The valley where the salt is extracted is thirty 

 miles long and fifteen miles wide. The nitrate undergoes a crude 

 washing in the valley ; it is then put into gunny bags and placed 

 upon the backs of mules for transportation to the coast. When it 

 is desired to procure a cargo the simplest way is to go at once to 

 Valparaiso to treat with the commission merchants, who will 

 undertake to have the order filled. The traders embark all of the 

 animals necessary to bring the soda, also their food, and even water 

 to drink, as the country to be traversed has neither vegetation nor 

 springs. It is a region of country which, at one period of our 

 geological history, experienced such a bombardment of meteoric 

 iron as the Avorld has never since beheld. Masses of iron weigh- 



