MEASUREMENT OF VARIABLE PROPERTIES 157 



growth ^ and represents the mean growth. On both sides of this 

 line the specimens (small dots) are distributed (according to the 

 law of errors) within a zone, which is limited by the greatest 

 errors ( + o-i and -O'l). This zone is the variation zone of the 

 curve of growth. 



2nd Series. — See below, p 157. 



3^^ Series. — The weight of the precipitate is determined in 

 the 200 portions and the curve of growth is constructed in the 

 same way as for the first series (Fig. 21). 



In the intervals I. -IV. everything happens as in the first 

 series, the curve of growth (thick dots) being, on the whole, 

 an obliquely ascending straight line. As soon as portion 91 is 

 reached (in the middle of interval V. ; see Table, p. 154) the 

 weight of the precipitate cannot exceed 1000 mgr, even if the 

 greatest possible positive error ( + o-io c.c, which coincides 

 with + 10 mgr. of precipitate) is committed. When portion loi 

 is reached the maximal value of the weight precip. (1000 mgr.) 

 is reached if no error is committed. (See Table, p. 154.) This 

 weight may be diminished by a negative error, but it cannot be 

 augmented by any positive error whatever. From portion iii 

 to the last one the value 1000 mgr. is certainly invariable ; it 

 cannot be modified even by the greatest negative error. There- 

 fore in the intervals VI. -X. all the small dots (with the possible 

 exception of the portions loi-iio) are situated exactly on a 

 horizontal straight line (second part of the curve of growth), 

 and here a zone of variation does not longer exist. 



Remark : The property weight precip. may be compared to an arrested per- 

 sistent property. (See § 46. ) 



2nd Series. — Here we find an example of discontinuous 

 variation (red, blue) which gives rise to a curve or line of growth 

 of a peculiar kind. In the intervals I.-IV. the acid is predomi- 

 nant whatever may be the errors, and the colour is always red. 

 When portion 92 is reached pipette B is expected to give 9 91 

 c.c. of alkali, but if a maximal error ( + 01) is committed the 

 volume B may reach looi, and since the volume A is lo-oo, 

 the colour of the mixture is blue. From portion 92 to iii 

 errors may produce an irregular alternation of red and blue. 



. . . rrrrrrrrrrrbrrbrbrbrbrbrbrbrbrbbrbbbbbbbbbbbbbbbbbb . . . 



1 92 111 200 



Fig. 22. — Development of the colours : r, red ; b, blue. (See text.) 



In all the portions 112-200 the alkali is predominant in spite 

 of any error whatever and the colour is always blue. In the 

 development of the property colour we can therefore distinguish 

 three periods (Fig. 22) — viz. red ; hesitation between red and 

 blue (alternative variation) ; blue. 



1 This curve is an embryological curve. (See § 49.) 



