We define the concentration range where a dilute alloy of transition impurities in a noble matrix is a spin glass, by the possibility of representing its properties through universal functions of the T/c and H/c variables. The susceptibility of a spin glass contains one reversible part Xr which shows a sharp peak at a temperature TM -- c. This sharp peak is due to the presence of a remanent magnetization which appears when T < TM. The remanent magnetization of a spin glass is represented by an universal curve in the reduced diagram CT~~/C = f (TIC). Its properties are like those of the remanent magnetization of monodomains. We interpret it by supposing that at T < TM a spin glass (in which the magnetic moments randomly distributed are frozen at T = 0 in random directions) is spontaneously divided in regions, each one containing in average n impu- rities and having a resulting moment Mg described by a Gaussian distribution (~7 = n,ui, where ,uo is the individual magnetic moment). 1. Introduction. - The properties of dilute solu- tions of transition atoms in noble metals (CuMn, AgMn, AuFe, &Cr, &Mn ...) can be understood Ktermsof a model, where a molecular field X, is created at the site of each transition atom, due to the R. K. K. Y. interaction between the magnetic mo- ments. In zero external field, and at T = 0, each moment is frozen in the direction of the field X on its site, and only the moments in a low field are sensitive to a small excitation (magnetic field, thermal agita- tion) (I). This disordered and frozen arrangement is now called a spin glass or a magnetic glass (2). Using an idea of Blandin 131, Souletie and Tournier (4) have shown that very general properties of spin glasses may be deduced from the l/r3 decrease of the R. K. K. Y. interaction, and from the invariance of the product cr3 (where c is the concentration) in a dilatation model. Thus, reduced quantities such as the magnetization (Mlc) and the specific heat (Cplc) can be represented by universal functions of the reduced variables Hlc and T/c (where His the applied