90 Professors Kirchhoff and Bunsen on Chemical 



chlorate of potassium which had been previously recrystallized 

 six or eight times. The chloride of sodium was prepared by 

 neutralizing pure carbonate of sodium with hydrochloric acid 

 and crystallizing the salt several times. The salt of lithium was 

 purified by precipitation fourteen times with carbonate of am- 

 monium. The purest specimen of marble which could be 

 obtained, dissolved in hydrochloric acid, was the source of the 

 calcium salt. From this solution the carbonate of calcium was 

 thrown down in two portions by fractional precipitation with 

 carbonate of ammonium, the latter half of the calcium salt being 

 converted into the nitrate. The salt thus obtained was dissolved 

 in absolute alcohol, and after evaporation of the alcohol, converted 

 into the chloride by precipitation with carbonate of ammonium 

 and solution in hydrochloric acid. 



In order to obtain pure chloride of barium, the commercial 

 salt was boiled out repeatedly with nearly absolute alcohol. 

 The residual salt freed from alcohol was dissolved in water, and 

 thrown down by fractional precipitation in two portions, of 

 which the second only was dissolved in hydrochloric acid, and 

 the salt still further purified by repeated crystallizations. 



The pure chloride of strontium was prepared by crystallizing 

 the commercial salt several times from alcohol, and by fractional 

 precipitation of the salt with carbonate of ammonium, the second 

 portion being dissolved in nitric acid, and the nitrate freed from 

 the last traces of calcium salt by boiling with alcohol. The 

 product thus purified was lastly thrown down with carbonate of 

 ammonium, and the precipitate dissolved in hydrochloric acid. 

 All these various purifications were conducted as much as pos- 

 sible in platinum vessels. 



The apparatus which we have usually employed for our 

 spectrum-observations is represented in the annexed woodcut. 

 A consists of a box blackened on the inside, the bottom of 

 which has the form of a trapezium, and rests on three feet ; the 

 two inclined sides of the box, which are placed at an angle of 

 about 58° from each other, carry the two small telescopes B and C. 

 The ocular lenses of the first telescope are removed, and in their 

 place is inserted a plate, in which a slit made by two brass knife- 

 edges is so arranged that it coincides with the focus of the 

 object-glass. The gas-lamp D stands before the slit in a position 

 such that the mantle of the flame is in a straight line with the 

 axis of the telescope B. Somewhat lower than the point at 

 which the axis of the tube produced meets the mantle, the end 

 of a fine platinum wire bent round to a hook is placed in the 

 flame. The platinum wire is supported in this position by a 

 small holder, E, and on to the hook is melted a globule of the 

 dried chloride which it is required to examine. Between the 



