TECHNICAL REPORT 7553 So Published 1987-07-01 Fertilizers -- Sampling -- Minimum mass of increment to be taken to be representative of the total sampling unit Engrais - Echantillonnage -- Masse minimale du prelevement en cas de traitement de la totalite de I'unite d'echantillonnage a prelever ISo (International Organization for Standardization) is a worldwide federation of national standards bodies (IsO member bodies). The work of preparing International Standards is normally carried out through IsO technical committees. Each member body interested in a subject for which a technical committee has been established has the right to be represented on that committee. lnternational organizations, governmental and non-governmental, in liaison with isO, also take part in the work. The main task of IsO technical committees is to prepare International Standards. In exceptional circumstances a technical committee may propose the publication of a technical report of one of the following types : type 1, when the necessary support within the technical committee cannot be obtained for the publication of an international Standard, despite repeated efforts; type 2, when the subject is still under technical development requiring wider exposure; type 3, when a technical committee has collected data of a different kind from that which is normally published as an International Standard ("state of the art", for example). Technical reports are accepted for publication directiy by Iso Council. Technical reports types 1 and 2 are subject to review within three years of publication, to decide if they ca s. Technical reports type 3 do not intoInterr nationalStandards necessarily have to be reviewed until the data they provide is considered no longer valid or useful. The reasons which led to the decision to publish this document in the form of a technical report type 3 are explained in the introduction. 0 Introduction Within the framework of its work on sampling, Technical Committee 134, Fertilizers and soil conditioners, has, through its sub. .committee 2, carried out studies on the minimum mass which an increment may have in order to remain representative of the fertilizel sampled. This work complements other standards for fertilizers, currently under preparation, particularly those which describe sampling plans for lots of various sizes, and those related to sample reduction. This study, which is different from those usually published as International Standards, is intended to act as a complement to them, as a technical report (type 3) for the sampling of fertilizers. ISO/TR 7553 : 1987 (E) UDC 631.8 : 620.113 Ref. No. ISO/TR 7553 : 1987 (E) Descriptors : fertilizers, sampling. @ International Organization for Standardization, 1987 Price based on 7 pages ISO/TR 7553 : 1987 (E) Scope and field of application When sampling is carried out on a batch of fertilizer, an increment is taken from N units. Each of these increments may be taken either by means of partial sampling devices, if their validity (absence of any particular bias) is assured, or by treating the complete item with a suitable reduction device (absence of bias). This Technical Report specifies, for the latter case, the extent of mass reduction beyond which the error in the representativity of the treatment of the sample, up to analysis. Where partial sampling devices are used, this limiting mass can be much more important. 2Basic. theory Taking into account the granular nature of solid fertilizers, the sampled mass cannot be reduced indefinitely without losing all representativity. However, it is possible to relate the mass of the sample to a minimum error of representativity, as a function of the variability in composition of the product sampled and of its particle size distribution. Emphasis should, however, be placed on the nature of the minimum limit value of this error to which can, in practice, be added targe errors due to the variability of the increments, often associated with defe