Shifting of axis title and sub-title in Gnuplot histogram - gnuplot

Question

Mr data file is
# test.dat
# Sample No. Phenol Red Neutral Red Bromophenol Blue Bromocresol Green Mixed Indicator
1 80 69 223 222 130
2 89 62 321 267 160
3 92 67 248 276 147
Gnuplot code is
#
#
###
reset session
###
set terminal postscript eps enhanced colour font 'Times-Roman,12' size 6in,4in
set output "test.eps"
#------------------------------------------------------------------------------
set style line 1 lt 4 lw 1 lc rgb "#4169E1"
set style line 2 lt 4 lw 1 lc rgb "#2E8B57"
set style line 3 lt 5 lw 1 lc rgb "#FF4500"
set style line 4 lt 4 lw 1 lc rgb "#FAD02C"
set style line 5 lt 4 lw 1 lc rgb "#FF0080"
#------------------------------------------------------------------------------
set xtics out scale 1.5
set ytics out scale 1.5
set ytics nomirror
set yrange [0:350]
set key off
set tics font ", 16"
set xlabel "Sample No. " font ",16"
set ylabel "Moisture Content ({/Symbol \155}g of H_{2}O/g of melt)" font ",16"
set key samplen 2 spacing 1.65 font ",14" width -1.0
set key inside left horizontal
set style fill solid border
set style histogram clustered gap 1 title textcolor lt -1
# ----------------------------------------
set rmargin screen 0.9
set lmargin screen 0.1
set bmargin screen 0.4
# ----------------------------------------
set style data histogram
plot \
newhistogram "Direct titration", \
'test.dat' using 2:xtic(1) ls 4 axes x1y1 title "Phenol Red", \
'' u 3 ls 5 axes x1y1 title "Neutral Red", \
newhistogram "Back-titration", \
'test.dat.dat' using 4:xtic(1) ls 1 axes x1y1 title "Bromophenol Blue", \
'' u 5 ls 2 axes x1y1 title "Bromocresol Green", \
'' u 6 ls 3 axes x1y1 title "Mixed Indicator"
# ----------------------------------------
##
Script works fine. I would like to provide more spacing between the tick labels (1,2,3) and the sub-title (Direct titration and Back-titration) as well as spacing between the sub-titles and axis title. How can it be done?

Answer 1

set xlabel offset 0, -1 will shift both the subtitles and the axis title downward by one character height.
set xlabel "\nTEXT" will create a two-line axis label and place TEXT on the second line.
Modifying your xlabel command to be
set xlabel "\nSample No. " font ",16" offset 0,-1
will make both those changes.