This standard specifies a routine method using black amide for the determination of the protein content of milk. As the composition of the amide black dye can vary, the method described is empirical and depends on a constant reference to the protein content deduced from the determination of the nitrogen content of milk by a reference method (UNE 34-823). The method is applicable to raw or treated milk (pasteurized, homogenized, sterilized, reconstituted), whole, skimmed, partially skimmed, as long as the samples are in a perfect state of conservation. It is also applicable, under certain conditions, to samples that contain preservatives (see 11.1). Serial determinations can be made. In this case, care must always be taken with certain special factors that are described in Annex B. NOTE — Depending on the origin of the sample and the reference method used, the amide black method described in this standard may be used not only for the usual determination of the protein content of milk (N x 6.38) but also for the determination of the "true protein" content and even, in a modified version, for the determination of the casein or whey proteins, both in cow's milk and in the milk of other animal species (goat, sheep, etc.).