Abstract: A method for the colorimetric determination of nitrate ions comprises mixing the sample to be investigated with concentrated sulfuric acid and adding a reagent which initiates coloration, the reagent being a compound of the general formula RO--C.sub.6 H.sub.4 --C.sub.6 H.sub.4 --OR, wherein R is H or substituted or unsubstituted C.sub.1-6 alkyl. A reagent and kit for colorimetric nitrate determination are also provided.

Abstract: A device for supporting sample-containing tubes in generally vertical parallel adjacency, one of the tubes containing an unknown sample and the other containing a reference or comparison sample, with the bottoms of the tubes located in predetermined relationship with a color table or chart having colored or shaded portions preselected and calibrated in accordance with the particular comparison to be made, the table or chart being movable at a right angle relative to the tubes such as to provide visual comparison between the samples based on color or optical density.