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should supply each of them with a prescribed sequence and an earnest plea that it be followed exactly. The data form should reflect the desired sequence whenever possible, and should always be constructed in a manner that will make entries easy when the sequence is followed. Sometimes it is impossible to apply a complete randomization scheme, as, for example, when one chemist is the expert on one type of equip ment while another man at the same activity is the logical choice for an other method or piece of equipment. Then a partial or compromise ran domization is all that is practical. Sometimes all the samples for two different operations can be weighed in a random fashion at the same period, thereby eliminating at least the possibility of time effects on the individual portions from the same sample. Replication. Too much replica tion causes a waste of effort; too little fails to give the required sensi tivity. Some guidance on replica tion is given in the American So ciety for Testing Materials publica tion D 1421-56T (3). When some practice has been had with a method and some knowledge exists as to the precision which it can show, then it may be found that only two or three replicates will be sufficient to provide the sensitivity desired in an interlaboratory test. It should be remembered, however, that programs conducted at this low level of replication are without benefit of a good means for detect ing and rejecting faulty data at the operator level as described in the following section. In the work of the Analytical Chemistry Panel mentioned above, five or six replica-
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for gamma irradiation of solids, liquids, gases continuous temperature control
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Victoreen Model 770 Radcell
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200,000 r/hr or more* Uses for Victoreen's new Radcell high intensity gamma irradiator are virtually unlimited for re search in the fields of chemistry, petroleum and biology. No specially shielded room is required. Exclusive turret loading principle assures operator safety. Source is surrounded by two metallurgically bonded coils: one provides for flow of fluid samples around source, the other provides for flow of refrigerated or heated liquids for precise temperature control of sample. A -ei9A *Us~'ng 1000 curie Cobalt 60 source. Shielding is adequate for 1,000,000 r/hr when loaded with sufficient Cesium 137. Write for your copy of Form 3024-9 "Victoreen Radcell Gamma Irradiator"
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