The Department of the Interior has a basic responsibility for the appraisal, conservation, and efficient utilization of the Nation's natural resources including water as a resource as well as water involved in the use and development of other resources. As one of the several Interior agencies, the U.S. Geological Survey's primary function in relation to water is to assess its availability and utility as a national resource for all uses. The Geological Survey's responsibility for water appraisal includes not only assessments of the location, quantity, and availability of water, but also determinations of water quality. Inherent in this responsibility is the need for extensive water-quality studies related to the physical, chemical, and biological adequacy of natural and developed surface-and groundwater supplies. Included, also, is a need for supporting research to increass the effectiveness of these studies. As part of its mission the Geological Survey is responsible for a large part of water-quality data for rivers, lakes, and ground water that is used by planners, developers, water-quality managers, and pollution-control agencies. A high degree of reliability and standardization of these data is paramount. This manual was prepared to provide accurate and precise procedures for the collection and analysis of water samples required for these needs. The series of manuals on techniques describes procedures for planning and executing specialized work in water-resources investigations. The maaterial is grouped under major subject headings called books and further subdivided into sections and chapters; Section A of Book 5 is on water analysis. The chapter on dissolved minerals and gases is the first in this series of chapters on laboratory methods for water-quality analysis. The unit of publication, the chapter, is limited to a narrow field of subject matter. This format permits flexibility in revision and publication as the need arises. Provisional drafts of chapters are distributed to field offices of the U.S. Geological Survey for their use. These drafts are subject to revision because of experience in use or because of advancement in knowledge, techniques, or equipment. After the technique described in a chapter is sufficiently developed, the chapter is published and is for sale by the Superintendent of Documents,