If $x$ gram of gas is adsorbed by $m$ gram of adsorbent at pressure $P$ the plot of $\log \frac { x } { \mathrm {~m} }$ versus $\log \mathrm { P }$ is linear. The slope of the plot is: (m and k are constants and $n > 1$)\\
(1) $\log \mathrm { k }$\\
(2) $\frac { 1 } { n }$\\
(3) 2 k\\
(4) $n$