January 23, 1903.] 



SCIENCE. 



153 



lected from the statuettes. The pale blue 

 rust can be best removed as follows: The 

 statuette is immersed in a bath of hot water 

 and live steam passed in for one hour to keep 

 the temperature up to 100° C. The sodium 

 carbonate is thus completely dissolved, the 

 blue color changing to black as the sodium 

 carbonate goes into solution. Careful brush- 

 ing from time to time facilitates the process. 

 After about one hour's treatment the metal 

 is exposed and the rust completely removed. 

 The dark green patina is not at all altered by 

 this treatment. Any loosely adhering frag- 

 ments of stucco can easily be preserved by 

 exercising a little ordinary care. 



The pale green excrescence resembles the 

 pale blue in almost every particular except 

 the color. It occurs in patches or layers 

 sometimes several millimeters in thickness, 

 and can be distinguished from ordinary patina 

 by its lighter color and more powdery appear- 

 ance. On chemical analysis it was found to 

 contain no sodium carbonate and to consist 

 mainly of copper carbonate. The removal of 

 the pale green corrosion is much more diffi- 

 cult and liable to damage the statuette. With 

 care, however, the following method gives 

 good results : The bronze is immersed in a 

 hot solution of five per cent, caustic soda for 

 several minutes. The green color imme- 

 diately turns to blue and the rust is loosened 

 sufficiently to be removed with a dull instru- 

 ment. Alternate treatment with the alkali 

 and mechanical scraping will finally remove 

 all of the corrosion. All of the alkali must 

 now be removed by careful rinsing, and if 

 necessary with a very dilute solution of hy- 

 drochloric acid. The dark green patina is 

 also removed by this process and an ancient 

 statue may acquire an undesirable appear- 

 ance of newness. 



The desirability of cleansing the bronzes 

 at all must also be considered. In the case 

 of the pale blue corrosion this seems neces- 

 sary, as considerable quantities of metal can 

 be destroyed by the action of the sodium car- 

 bonate. In the case of the pale green the 

 destruction of the metal does not take place 

 as rapidly, and other factors must be consid- 

 ered. If the bronze is to be used as a show 



specimen it is better to leave it unchanged 

 in its antique appearance. For purposes of 

 study, however, a complete cleansing of the 

 surface is necessary, as tracings and engra- 

 vings have often been exposed which otherwise 

 might not have been revealed. After cleans- 

 ing the statues should be kept as much as 

 possible in a dry atmosphere. Statuettes in 

 the Boston Museum cleansed by the above 

 methods and placed in air-tight cases have 

 not again become corroded. Some imple- 

 ments are made of very thin metal, and the 

 removal of the thick layer of corrosion would 

 leave too thin a shell. Such cases must be 

 individually considered, and it is better not 

 to place the responsibility of cleansing val- 

 uable bronzes in unreliable hands. 



Waldemar Kooh. 

 Chicago, III., September, 1902. 



NOTE ON THE CIRCULAR SWIMMINO OF SAND- 

 DOLLAR SPERMATOZOA. 



While studying artificial parthenogenesis 

 in the sand-dollar {E chinarachnius parma) 

 during the past summer, the writer indepen- 

 dently observed that when the spermatozoa 

 of this species are placed in a drop of sea- 

 water on a slide they "nearly or quite all 

 gather at the upper and under surfaces of the 

 drop and move there in circles. As seen from 

 above, those at the upper surface move in a 

 clockwise direction, and those at the under 

 surface in a counter-clockwise direction. That 

 is, since the head of the spermatozoon is di- 

 rected towards the surface of the water, con- 

 sidered from its position the motion is always 

 counter-clockwise. 



This motion is so conmion as to seem at 

 times to be universal, and it occurs without 

 regard to the presence or absence of a cover- 

 glass above the drop. The circle is approxi- 

 mately constant in size, having a diameter of 

 about the length of the spermatozoon. 



This attraction of the spermatozoon to the 

 surface of the drop apparently shows it to be 

 strongly stereotropic. Two possibilities sug- 

 gest themselves as explanations of the circular 

 motion. One is that the spermatozoon is dif- 

 ferentiated in two planes, so that it has what 

 may be called dorsal, ventral, right and left 



