A method is described for the spectrochemical determination of Si, Na, K, Al, Ca, Mg, Fe, and Mn in minerals, rocks, slags, and related substances; the determination of Ti is also discussed. The d.c. carbon arc is employed. One part of powdered sample is mixed with 1 part of SrCO3, which serves as internal standard for the determination of all the elements mentioned except Si, or with 2 parts of quartz and 3 parts of SrCO3 if a more diluted sample is wanted. For the determination of Si the mixture is 1 part of sample +1 part of BeCO3 (internal standard) +3 parts of NaCl. Carbon powder is added to all the mixtures. Three arcings are necessary: for K and Na in the visible and upper ultraviolet region with the sample in the cathode; in the ultraviolet for Si, also with cathode evaporation; another in the ultraviolet for Al, Ca, Mg, Fe, and Mn (and Na) with the sample as anode. The use of different sized electrodes is discussed. Calibration curves are shown, based on the spectra of actual minerals, rocks, slags, etc. having reliable chemical analyses. The relative error is in most cases less than 10 percent.