library(corrplot)
library(readxl)
chemistry <- read_excel("chemistry.xls")
plot(chemistry$pH, chemistry$O2mgL, xlab="pH", ylab="O2 in mg/L", 
   pch = 19, lwd=1.5, cex=1.5)
# multiple scatterplots
pairs(chemistry[, c("pH", "TWasC", "O2mgL", "ClmgL","NO3mgL" )])
# For correlatioin plots only numerical variables can be used
# Therefore we create a subset of the numerical variables chemistrynum
# by substracting the first and second column that contain depth and location
chemistrynum <- chemistry[c(-1,-2)]
# The correlation plot helps to identify the type of correlation
corrplot(cor(chemistrynum))