102 Professors Kirchhoff and Bunsen on Chemical 



are not attacked by that acid, the following method may be best 

 employed for the detection of calcium. A few milligrammes of 

 the substance under examination, in a state of fine division, are 

 brought upon a flat platinum lid, together with about a gramme 

 of fluoride of ammonium, and the mixture is gently ignited until 

 all the fluoride is volatilized. The slight crust of salt remaining 

 is moistened with a few drops of sulphuric acid, and the excess 

 of acid removed by heat. If about a milligramme of the resi- 

 dual sulphates be scraped together with a knife, and brought 

 into the flame, the characteristic spectra of potassium, sodium, 

 and lithium, supposing these three metals to be present, are 

 first obtained either simultaneously or consecutively. If calcium 

 and strontium be also present, the corresponding spectra gene- 

 rally appear somewhat later, after the potassium, sodium, and 

 lithium have been volatilized. When only traces of strontium 

 and calcium are present, the reaction is not always seen ; it be- 

 comes, however, immediately apparent on holding the bead for a 

 few moments in the reducing flame and, after moistening it 

 with hydrochloric acid, again bringing it into the flame. 



These easy experiments, such as either heating the specimen 

 alone, or after moistening with hydrochloric acid, or after treat- 

 ing the powder with fluoride of ammonium, either alone or in 

 presence of sulphuric or hydrochloric acid, provide the minera- 

 logist and geologist with a series of most simple methods of 

 recognizing the components of the smallest fragment of many 

 substances (such, for instance, as the double silicates containing 

 lime) with a certainty which is attained in an ordinary analysis 

 only by a large expenditure of time and material. The follow- 

 ing examples will illustrate this statement. 



1. A drop of sea- water heated on the platinum wire shows at 

 first a strong sodium reaction ; and after volatilization of the 

 chloride of sodium, a weak calcium spectrum is observed, which 

 on moistening the wire with hydrochloric acid becomes at once 

 very distinct. If a few decigrammes of the residual salts ob- 

 tained by the evaporation of sea-water be treated in the manner 

 described under lithium with sulphuric acid and alcohol, the 

 potassium and lithium reactions are obtained. The presence of 

 strontium in sea-water can be best detected in the boiler-crust 

 from sea-going steamers. The filtered hydrochloric acid solution 

 of such a crust leaves, on evaporation and subsequent treatment 

 with a small quantity of alcohol, a residue slightly yellow- 

 coloured from basic iron salt, which is deposited after some 

 days, and can then be collected on a small filter and washed 

 with alcohol. The filter, burnt on a fine platinum wire and held 

 in the flame, gives, besides the calcium lines, an intensely bright 

 strontium spectrum. 



