NEW BOOKS Photographische Probleme. I?j, Lifppo-Civrrzct.. (Eiicj'bloplidir d c r Photogra#ilic. Heji jb'.) I J x 2 2 c v i ; p,b. ; i + 2 2 0 . Haiic: I T i l i z c l m KnaP,b, 190;. Price: pLiper, ?..io ~tziii.ks.-This volume is based on the papers ~ ~ u l ) l i ~ l i e d b y the author during the years 1902-1907. The subject is discussed under t h : headings: ripening of the emulsion; ~ihotocheriiicnlchanges; the so-called chemical fog ; the phenomenon of solarization ; the pliotohalides or' Carey Len. Under the ripening of the emulsion the chief points of interest to the author are the effect of the size of the grain and the so-called theories in reyard to sensitizers, Under the heading of photochemicnl changes .,ye iind n discussion of the nature and reactions of the latent image. By chemical fog tlie author means the state of a silrer bromide emulsion 11-hich can l x de\eloped vitliout exposure to light. The author tries to prove t h a t this state is different from t h a t of a normal plate 17-hich has lieen fogged b y exposure t o lig-lit. In the article o n solarization the author's aim is to show t h a t all the theories of solarization are worthless and t h a t . \ h e y ' s is nearly the norst of them all. I n the section on pliotohalides the author explains his lielief t h a t these substances are "adsorlition coniliounds of silver halide and silver" and t h a t they are identical with the substance forming the latent image. This last is the one l i t of constructire work in the hook. \i71iile the volume is a n exceedingly interesting one, i t must he a bit discouraging to most people. I t may lie t h a t the author k n o m too much about the sulijcct or i t may lie a temperamental matter; b u t the fact remains that the author's attitude is represented by one of du Bois-Reyniond's catchwords: " I g i ~ ~ ~ a ~ i i { . zTo . " the reviewer things do not seem so bad. I t seenis to him t h a t many of Liippo-Cramer's experiments can he explained in a way quite different from t h a t adopted in tlie text. If that is done consistently, the photographic prolilems lieconie quite simple ones-at a n y rate to one, like the reviell-er, who is certainly not handicapped liy a n extensive practical knoll-ledge of the subject. I l - i l d o . D. Ga,zci.ojt The Theory of Valency. By J . .YcrLtoji Frictid. Edzted h j . Il-iiiium IZoiiz12 X 19 ciiz; p p . i x 180. -\-L-L I - o r k : Lo,iqiiiuits, Grren 2 Co., 1909, Pricc: S1.6o.-The author devotes one chapter to the early theories of chemical combinations and another to the early theory of valency. Then lye have two chapters on valency and the periodic law, folloved by a series of chapters on the valency of the different elements. One chapter is devoted to IYerner's theory, another to electrochemical theories, and the last one to a discussion of the physical cause and nature of valency. The author accounts for such formulas as Cu,CI,, Hg,Cl, and others by considering the chlorine a s trivalent. I t is claimed t h a t nickel acts only as a divalent metal, 11. 11;: on the other hand cobalt and iron are permitted tu lie 110th divalent and trix-alent, 11. 3.1. I n view of the existence of hydrated nickelic oxide in the Edison cell, this seenis to be a n arbitrary and therefore a n un\\-ise distinction. The fact. t h a t ammonium arnalgam vvill precipitate metallic copper from a solution of a copper salt I\-ould seem to lie pretty strong evidence saj'.
+
t h a t there was something in the mercury besides ammonia and hydrogen, p. 83. On the other hand the author is \Tilling to believe in the existence of t h e imaginary substances, CuAl and Cu,rll, p. 15j. I n the chapter on the physical cause and nature of valency, the follon.ing paragraphs, p, 167, seem worth quoting: " I t is well known t h a t the numerical values of the valencies of those elements which exhibit variable valency usuaily differ by two, or multiples of t w o units. Thus gold is mono- and tri-valent. Sitrogen and phosphorus are triand penta-valent. Sulphur is di-, tetra-, and hexa-valent. So long as the old ideas prevailed, that the atoms were provided with hooks and eyes, which represented their valencies, a physical interpretation of the above v-as clear, B u t the demolition of these crude notions has rendered the explanation of multivalency more difficult. "The suggestion of Barlon. and Pope is, to say the least, very ingenious. Imagine a n assemblage of close-packed spheres, and let one of these spheres have a valency volume m. If this is removed, and into the cavity thus produced a sphere of \-olume vi - I is pushed, i t will be clear t h a t a second sphere, of valency volume I , must simultaneously be introduced into the enveloping shell of atoms, if the close-packing is to be restored without remarshalling. This is obviously equivalent to the insertion of an atom of valency I in the space already occupied b y a n atom of valency m,and the filling of the gap t h u s produced in the enveloping shell by the insertion of a second atom of valency. I. The atom of valency i n will thus function as an atom of valency in i2 . Similarly, b y pushing two atoms of valency I , or \That conies to the same thing, an atom of valency 2 , into the space already filled by a n atom of valency )n either t x o atonis of valency I . or one of valency 2 , must be inserted into t h e enveloping shell. Consequently the atom originally exhibiting a valency tn, now functions a s a n atom of valency v i 1. Sulphur is a case in point. " I t has already been pointed out, however, that all atonis exhibiting the same valency have not exactly the same valency volumes. For example, as a n y vertical column in the Periodic Classification is descended, a slight change in volume is exhibited, nltliough it is not sufficient to change the valency by a whole unit. If, therefore, atoms of valencyvolume exactly equal to unity are combined ivith other atoms of \-alency-\-olume intermediate between t w o whole members, i t is clear t h a t various assemblages may be formed. in which the numbers of monuvalent atoms attached to one of the polyvalent atoms will not always difier b y two. Llolybdenum is a good example of this, for the di-, tri-. tetra-. and penta-chlorides. JIoCI,, JIoCI,, JIoCI,, and LloC15, respectively, are known." The author had a good subject and he has written a useful hook; b u t t h a t is all t h a t he has done. The I~ool;is merely one of the series and nothing more. 1 I .ildcr D , Uaiiwojf.
+
MCthodes de CalorimCtrie. Crifhcs nu Lnboratol'w Therwiique de l'L.)zzuersitd tic .lioscou p a r I T . Loi~qu2'1~I'?zc ct A , S c i i u k a r e ~ . Tmdirit d e la Russc pur G. T c v Gazariail. 18 X 27 c m ; pp. 192. Paris: A. Hermaim. Gerzix: Georq Co., 1908. Price: Liiicn, 8 jravcs.--Ostensibly this is merely a book describing the methods of calorimetry in use a t the Xoscow laboratory b u t actually
