322 R. Bunsen on the Washing of Precipitates. 
ential quotient equal to 0, then the minimum value of W be- 
comes, when n= o, 
Wer net 10g, G6 |< oe 
Precipitates obtained in the course of chemical analysis may 
in all cases be assumed to be sufficiently washed when the im- 
? 
Pp 
equation (4) that the least quantity of fluid required in order 
by the precipitate itself in the liquid in which it exists. It 1s 
evident, therefore, that the amount of water actually necessary 
to wash a precipitate the more nearly approaches this minimum 
the oftener we decant, and the smaller the quantity of washing- 
water we employ at each decantation. : 
Since some of the principal sources of error in analytical 
work consist in the incomplete or in the too protracted washing 
of precipitates, it becomes important to know how to ascertain 
the progress of the washing throughout the several stages of 
the process. By employing the same volume of water at eac 
successive addition, and est mating its relation to that of the 
precipitate remaining at th bottom of the vessel or upon the 
ter, we can find from the following Table, calculated by 
STckeKS Sowa ’ oie oe 
Tovove- svouT- zooDN- T3v0o" 
Be | oe eee ec oat doe | II | I t pee 
a eee ae we oe oS oe ee 
v v 9 oD 
05) 24 | 142] 05) 267 | 138 | 05! o44 | 122 | 05) 227] 14 
1 | 166 | 166] 1 | 156| 1561 1 | 443! 143) 1 | 133 | 188 
2 | 105/ 20] 2 | 98| 107] 2 | gol agoll 2 | 84 | 163 
8 | 88/49] 3 | 73} 341 3 | 7| a4] 3 | 66| 199 
4 | 71| 86] 4 | 67| 691 4 | 611 a6 4 | 57] 29 
5 | 64| 3211 5 | 60] 3021 5 55 | 76] 5 | 51) 297 
6 | 59! 35] 6 | 56! 9341 6 | 51! 305 6 | 47 | 284 
7) 55| 338] 7 | 52] 364] 7 | 48] gall 7 | 44] 310 
8 | 531 40] 8 | 49| 9941 8 | 45| 361) 8 | 42} 3389 
9 | 50/450] 9 | 47/ 423] 9 | 43| 387] 9 | 40 | 360 
10 | 48/ 40] 10 | 45 | 451/10 | 41/| 413] 10 | 38 | 388 
| 46) 510} 11 | 44] 479] 11 | 40| 438] 11 | 37) 20% 
2 | 45 | 53-9 | 12 506 112 | 39 | 463] 12 | 36) o 
118 | 441] 564] 13 1| 533/13 | 38| a8] 13 | 35 | 4° 
if | 42) 504 | 14 40 | 55:8 || 14 87 | 511 || 14 34 Vt 
42 | 623 | 15 9| 585115 | 36/536] 15 | 33) 25 
16 | 41) 60/116 | 38| 61] 16 | 35 | 560] 16 | 33} 539) 
| 40) ersiiit | 37/636 | 17 | 84| 583] 17 | 32 | 583 
| 39) 4) 18 | 87] 661) 18 | 34] 605] 18 | 34 | pe 
19 | 33| 4319 | 36/6619 | 33} esi 19 | 31) 8 
means of the formula above given, the number of times it, 38 
necessary to decant in order to diminish the amount of impurity 
in the precipitate to the ; 
? Bs 
TOGTS2 FeGTe) Fosse OF TITTT 
er 
