The fact that in this particular instance the comparison of fluid levels assisted in determining the source of damage to the entire group of wells emphasizes the value of determining the head of water not only when is first encountered, but also at subsequent dates.
The purity of water, or rather the degree of its impurity, is frequently a definite clue to its underground source. In one locality, for instance,' the water lying below a certain oil zone carries about twice the amount of dissolved mineral salts as does the upper or overlying water. Chlorides and carbonates pre dominate in the lower water, while sulphates predominate in the upper water. It should not be understood that definite propor tions are to be expected in all localities. However, careful com parison of water samples in any field will frequently develop some rule for that locality.
Determination of the purity of water does not always require a chemical analysis. Taste and odor will frequently serve to differentiate between two samples of water. A correct and complete log of a well should always mention such simple characteristics.
After a well is completed, or after several water bearing strata have been penetrated, it may be difficult or impossible to obtain separate samples from each stratum; therefore, the observations should be made while drilling is in progress.
Complete and accurate analyses of water encountered in drill ing will undoubtedly lead to the discovery of conditions having economic importance, and should be made, wherever Simple tests yielding incomplete information as to the chem ical content of water have been found useful, because they can be made quickly and require very little apparatus. They may be devised to determine the percentage of chlorides, carbonates or sulphates. After slight practice and instruction these tests can be made by persons having little or no technical knowledge of chemistry.
Short-cut methods of water analyses may not receive the approval of some analysts, but they are unquestionably justified for the purpose here mentioned. Investigation of quick methods of water analysis was made by M. 0. Leighton,' and his introduc tory remarks are worthy of quotation.
chemist aims to secure exceeding refinement in analytical methods and results. He seldom considers whether or not a method is sufficiently exact for certain broad purposes. The fact that it is incomplete, approxi mate, or susceptible of refinement is to him sufficient reason for im proving or rejecting it at the first opportunity.
"The scrutiny to which chemical methods have been subjected in the endeavor to secure exact results has led in many cases to processes so complicated and expensive that in commercial work the advantages do not compensate for the increased cost and delay which the methods involve. The result has been that the chemical profession distinguishes between two classes of chemical methods which differ in degree of ac curacy. The first includes the exact methods, which afford results as
nearly perfect as chemical procedure will permit. Such methods are used in all cases where minute differences in analysis would cause errors in interpretation or in subsequent chemical procedure. The second class ocnsists of "commercial methods," so-called because the results obtained by them, while departing from the actual truth, are sufficiently accurate to insure the profitable conduct of industrial chemical processes without appreciable error or waste. Methods of the first class are the product of chemistry while those of the second are used in response to the demands of expediency—they are good enough for the purposes for which they are used.
"In no branch of chemistry are approximate results more serviceable than in the analysis of water for hydro-economic surveys, or surveys made to determine the value of water and its applicability for use in domestic supply, boilers, industries, etc. Under the conditions which generally prevail it is necessary to resort to long, tedious and expensive processes in order to secure a determination of the character and amount of foreign constituents in water. It is the practice in such cases to secure a sample of the water and transport it to a laboratory, where, after conventional delays, it is passed through the usual course of analysis.
"There has been surprisingly little discrimination used in the past with reference to the selection of determinations for specific and as a general rule the same procedure has usually been followed with out regard to the object of the particular investigation. If the purpose of the analysis is to determine the incrusting constituents, the course pursued has been to follow the entire analytical procedure. If, on the other hand, it is desired to determine the amount of organic pollution in a water and show its value for domestic use, the chemist forthwith begins the round of nitrogen determinations, and closes with a statement of the oxygen consumed and the number of bacteria per cubic centimeter. In only a few well-known laboratories has this rule been violated, and such is the conservatism in the chemical profession that it will probably be followed largely in future. Conservatism is the safeguard of science and one of the most commendable qualities of a chemist, but an excess is sometimes almost as bad as a deficiency." It is unnecessary to outline here methods of water analysis as the subject has been well covered in many publications,' but the details of testing for chloride will illustrate the comparative sim plicity of the work and encourage a more general use of chemical The solutions can be standardized at a laboratory and furnished to the field observer who can quickly make the necessary tests.