This article describes an electronically controlled recording balance for obtaining, concurrently with the differential thermal analysis record, the weight record of a sample during heating. The apparatus is used for the study and for the determination of the quantities, by weight, of calcareous and hydroxyl components in materials. The instrument is capable of determining quantitatively the weight of active materials to within 6% of the sample weight by measuring the area under the peak of the differential thermal analysis record and to within 0.5% from the weight record. Some results obtained are presented and discussed.