The receiitly :iiii~o~inced tletcctioii :tiid Iiiensiireinent of hcliuin formed in the :irt,ificinl disilitegritt ion of boron by neutrons (Piinctli aiitl Loleit, Xuture, 1935, 136, 950) is one of the fcv-iiistitnccs in \vliicli such it process has beeti verified directly. 111 the early tlitys of riidioactivity, Rnins:ty rititl Soddy were i i l ) l ~ to show that tlic gases evolved froiii R solutioii of rndiuin broiiiide in w t c r coiitniiietl hcliuiii iii addition to hydrogen a i d osygcn. The lut,tcr irere formed by the dissociatioii of \.iitcr uiider bombitrdiiient due to the radioactive disintegration. They were reiiiorcd by contact with n red hot copper spiriil, iiiitl tlie spectruni of tlic small artiouiit of resitliiitl gits showed the lines of helium. There is very little doubt thilt this heliiir~i iirosc during the disiiitcgritt.ioii of t.lw riidiuiii, and that it \viis ciiiitted, in the first, plwe, :IS a-particles.
The nrtificid disintegriitioii of iitoiiiic iluclci was first observed in 1919 by Riitlierford aiid Chadwick. This process was brought about by boi~ii)artliiig soiiie of the lighter cleiiieiits with a-piirticles. The type of disi~itegriitioii \vliicli occurs is well illiistrnted 197 t,hc ciisc of nibrogcn, froiii \vliich II positively charged hpdrogcn atom is ejected with high \docity. This process w s stiidicd hy obscr~i~ig t,hc sciiitillatioii produced on n zinc sulpliitlc screeti hy the impact of ciich ittoill. 'l'hc iiiitiirc of tlic! particles wns itiferred from their ritiigcs iiiitl from t.lie deflection which they suffmd in clcctricrtl fcltls. h t e r t.he disiiit.cgriitioii process \VIM rccortlcd pliot,o-grnpI~icnlly by iiicitiis of the \'ilson cloiid apprtratus. Tllc question iiittiirnlly arises 11s t o whctlier the hydro-gel1 produced in sricli n. tlisititcgriit,ioii process criii also be tlctectctl s~~ectrnscopicrilly. Its ittnoiiiit is very s~iiull, iilid it Itas 1)ccii sliowii by I'riii~t~li itrid Gulrter that co~isidcriil~ly greater qimitities of Ilydrogeii t,li:tn t h e fortiled in t.lic itt.oniic tlisintcgration process i 1 1 ~1 y rcritlily Iic tlcrivctl froiii tlic walls of the glrtss iijipiir:ittis ii~id from tiip grcii~e. I t is doiil,tfiil tlicrc!forc if the! prodiict ion of Iiytlroi n sucli :I t1isitit:yittioii will c \ w lie sliowi directly.
't'lic recent tliscovcry of tlic ~~lictioiiicnii of iirt iliciiil rudioiictivity by Citric r i d Joliot his iitltlctl yet. :illot,licr c1iitl)tc~r to t,hc dory of ;it oiiiic syrit Iicsis,